I have been with my boyfriend for 5 years and everything has been good until recently. Our sex life has been very good but I have felt a bit bored over the last 8 months or so. I have casually mentioned this to him, not said I'm bored just said perhaps we could do some more adventurous stuff together. I have come up with ideas but he is always apathetic about them and when I asked him about his fantasies he refused to discuss them.

Really if a woman discusses her sexual fantasies with a guy, that should be treated as nothing short of amazing.  In fact if a woman says she wants more sex and wants to do it differently a guy should take notice and treasure that woman.  Far too often women sit back and let the guy decide what to do in bed and eventually that becomes boring to the guy, because he will run out of ideas.  In this case you are actually trying to help him out and he is not paying any attention to you.  This is wrong of him, he should be motivated to satisfy you and motivated to try different things in bed. 

The thing that sends alarm bells into my head is that you have been together 5 years and after that long together men can sometimes become lazy in a relationship, not just sexually but romantically as well.  Men just seem to think I've got her now, she's staying with me, so I don't really need to make too much effort anymore.  In recent years women are rebelling against this sort of attitude and either making there guys buck up their ideas or moving on to another guy.  So he certainly doesn't have any room for complacency, because if his laziness continues you could well find a better man. 

He said he has them but wouldn't say.

Men have a problem about discussing their sexual fantasies with women.  Their sexual fantasies are usually a lot different from women and when a man discusses them with women, the women usually says something like "that's disgusting or you weirdo".  A man learns at an early age that even if a woman asks you about your sexual fantasies, never tell her, because it usually turns her off, no matter how keen she was to hear them in the first place.

I left it at that. However, I am getting bored of the same routine all the time and shy away from sex more now if he tries it on, which is nearly every night!

That's the right thing to do, in fact if he's getting complacent with you, you should keep emphasizing your fantasies and abstain from sex until he is willing to fulfill them.  It could be that he feels pressurised by your demands or it could be that he is being lazy.  Either way he should be able to get over it and get on with it.

He just seems to want more of the same standard boring sex. I want to do more exciting things with him.

You really should be a dream woman to be with if you tell a guy what you want.

Recently I found a video and magazines under his bed and decided to look at the stuff one day when he was on his way upstairs. I have never had a problem with pornography and he knows this and this is one of the things I suggested we try. He came into the room and I was really up for it but he grabbed the stuff off me and told me to go home.

Men tend to feel ashamed about masturbation and looking at pornography, they certainly don't want their girlfriends to find their mags or videos, it's just embarrassing.  As well as being that buzz that he can have when he hasn't got a woman, it's also his inspiration for sex, so that maybe another reason why he doesn't want his girlfriend checking them out, because he might have tried a few things on you (though judging by how bored you are with him maybe he hasn't).  What's also in these videos and mags are things that he can't have in real life, they are fantasies that will never happen.  For example how many times is he going to be having sex with three women at once etc.  They are fantasies he wants to keep secret from anyone else.  Because again if he got down to talking about them, he would probably think that you would think they are disgusting ideas.

I was really angry with him for being like this when I had made it clear I had no issues with it. I stormed out and said you never want to do anything exciting in the bedroom, most men would love a girlfriend like me. I didn't hear from him for a couple of days and no way was I chasing after him. When he did ring he said that it was his private stuff and what he watched in private was his business.

That just emphasizes his reason for not wanting you to see it.  He feels this is a private part of his life that he doesn't want you to see, it messes up his head knowing that you have seen it and knowing that you have deliberately interfered into a private element of his life.

Feeling even more angry and hurt I went round to see a male colleague who I get on well with and explained the problem to him. He said what I had said to my boyfriend that most men would kill for a girlfriend like me. He told me he had always fancied me and we had sex. Well the sex was totally amazing and I realised what a rut me and my boyfriend had got into and it was obvious other blokes could satisfy me better than him. It is clear my colleague wants a relationship and has asked if I've told my boyfriend yet that it's over.

That gives a clear indication that he is serious, if he wasn't serious about your relationship he would be happy to be just getting some sex and for you to go back to your boyfriend to fulfill the rest of the relationship.  He could use your boyfriend as an excuse for your relationship with him to be not so serious.  But in this case he has stated clearly he wants your boyfriend out of the equation and for you to hook up with him.  It also points to a man that is willing to discuss and listen to your sexual needs and provide what you want.

I said well no and he said he won't share me with him which is fair enough. I now feel terrible when I see my boyfriend but have since slept with my colleague again and it was even better than the first time.

Sex is one element of the relationship, the other is whether his personality is compatible with yours long term.  You could find you have a guy that's a sex machine but doesn't have the right personality, then a boyfriend that is useless at sex but your long term soul mate.  Ideally you want to find a guy that's good at both.

I'm confused by what my boyfriend has said and can't understand him.

Really, I can't understand him either, it's almost like he doesn't want to put that much effort into your relationship anymore, as if he is either not interested in the relationship or doesn't think you would leave him because of all this.

I feel like I want to give the other man a try but feel eaten up with guilt. I'm not sure I love my boyfriend anymore and am certainly not prepared to have a substandard sex life when I know I can get it elsewhere and it's brilliant.

Really that's your perception and that's my perception to, if I had this problem with girlfriends, I know I would choose the woman that's good at sex, as long as her personality was right for me as well.  If the personality wasn't right then there would be no point in leaving your partner because basically you would break up with your partner and hook up with your new partner only to find out in a few months time that their personality is unbearable. Then you will be left with no partner at all.

Why does my boyfriend only seem to want and be happy with same old same old sex all the time?

He still has an appetite for sex, because you say he tries it on every night.  So I am guessing that he is obviously getting something out of the sex for himself and indeed guys don't need any foreplay or any kind of play whatsoever to get a buzz out of sex.  So basically he is getting what he wants from sex but failing to satisfy you.  For some reason he seems happy with satisfying himself or feels he is unable to do the things you want him to do.

If you hadn't told him about it in plain english then he would have an excuse for not making any effort to fulfill your fantasies but you have told him about it and told him what you want, so really he has no excuse whatsoever. 

Would I be wasting my time trying to make him do more things?

I think you can pretty much say that your relationship with him is breaking down, and therefore you can take some risks in trying to get him to do what you want.  You can have a go at repeating what you have already said to him and hopefully he might buck his ideas up.  But really if a guy is not satisfying you in bed, you don't want to spend the rest of your life with him, especially if there is another good opportunity available to you at the moment.  I don't know what your sexual fantasies are, but maybe you can take command in bed and make him do those things, it all depends on what you sexual fantasies are about.  Maybe you could also try telling him, if he doesn't improve then you are going to find another man, he won't be too happy with that comment but maybe it might encourage him to make more effort with you.

Shall I just cut my losses and start a relationship with my colleague?

At the moment that seems like the best option because your boyfriend is just not making any effort.  But I don't know how long you have given him to come good, it's up to you to judge whether you can give him some more time.  But really as long as you see your colleague as having a good personality, he is looking like the best option at the moment, in my opinion.