Why don't I want to have sex with my girlfriend anymore?

I've been with this girl for 5 years. We started out having great sex, all the time, at least 3 or 4 times a week, depending on how often i could see her. But it wasn't just about the sex, we were both very much in love. We felt like we could tell each other anything, and we never had to have any secrets. We were both very committed to each other, and although we had our differences sometimes, we put up with them, because we both knew that we were worth it. But then, 2 years ago I got lost in a drug addiction for about a year, so we almost never had sex. Don't get me wrong, she stayed by my side, didn't judge me, cared for me, and encouraged me. Basically everything I could ask for. 1 year ago, I started getting clean, and a doctor prescribed me medication that has a side-effect of lowering your sex drive, but usually only in the first few months of taking it. They weren't joking. We never had sex for 6 months. 6 months ago, that side effect seemed to disappear, and we started to have sex again. Everything was going great, until she became friends with a girl at her college. She started going to clubs every weekend with this girl, dressing in very revealing clothing, doing drugs (although I must admit, she is able to do hard drugs much more responsibly than me). Then she and this girl decided to go on a weekend trip to Montreal (we live in Toronto, so its not far). Basically to do the same thing, go clubbing. She came back, and she told me she cheated on me; with that girl. She claimed that she didn't really enjoy it, and that it was a one time thing, but she still goes clubbing with this girl, and I would think that if what she said were true, it would make the relationship too weird to continue.

Now she wants to have sex with me all the time. We'll be watching TV, and then she'll suddenly be on top of me. But for some reason, I just don't want to. I'll still get an erection, but I just can't see myself wanting to. Don't get me wrong, she's extremely attractive. She gets into clubs without paying or waiting in line, every time. She can't walk down the street without getting hollered at. But if I choose to have sex with her, I feel like I'm just doing it for her. She'll often leave right afterwards. If I say I don't want to, she gets pretty upset. She never says anything about it to hurt my feelings, but I can see it in the expression on her face that she isn't happy. I can honestly say that sometimes it feels like that is the only reason she sees me. I should point out that sometimes I feel attracted to other girls, and I still enjoy masturbation, so I know that the medication is no longer affecting my sex drive like it used to.

This is starting to drive a wedge between us. We've been through so much together, I would hate to see it end like this. I would greatly appreciate any advice you can give.

Wow, so much said in that small paragraph. Well I'm glad to see that you kicked your drug addiction, and sorry to see that she fell into one. I absolutely see your point about not believing what she is saying about her relationship with the girl she is with all of the time. I too think that after having a failed sexual encounter with a friend that things would be too weird to continue the friendship. Chances are she's still sleeping with her. She probably told you because she thought that you had figured out what was really going on. She probably figures she'd tell a half truth so that she looks only partially guilty, and then hope that you'd forgive her and move on (which it looks like you did). The random, frequent, and seemingly loveless sex (you said she usually leaves immediately after sex) is an unfortunate sign of a guilty cheater. Some cheaters try to compensate for their treachery by buying things for their partner, while others will try to f*ck them much more often. Both are attempts to make the cheater feel better about what they are doing to their partner. They feel that if they do more of what you want (or have sex more with their partner than the person they are cheating with) that it somehow makes things right/equal or makes them less wrong. Its a twisted way of thinking. Her sex with you has become payment/restitution in her eyes, and when she feels like she has "paid" you or "done her duty" she leaves. That is also why she gets mad if you say "no". She isn't able to unburden her guilt.

As far as your feelings and not wanting to end your relationship simply because you've been through so much.... If the love isn't there anymore it just isn't there. Sure she may have stuck by you when you had an addiction, but you didn't cheat. Had her situation been only about the drugs I'd suggest staying by her side because there was still love there and because she did the same for you, but there is another person involved here. No matter what went on in the past or how good things used to be you have to look at the present and the future. If someone else is coming between you two, you are losing desire for her, she is obviously still cheating (emotionally and/or physically), and she is still doing drugs what does the future of your relationship look like? Bleak at best. If she can cut this woman off, and start trying to get clean then you two have a chance. If she doesn't want to do BOTH then you need to move on and let her shoot heroine while her friend munches her pu*sy. (sorry in advance if any female members are offended by that word)

I suppose, in answer to your original question "Why don't I want to have sex with my girlfriend anymore?", that you realize that the love is gone from your relationship which decreases your drive to have sex with her. Before you were making love and now its just sex, which obviously isn't enough for you. Don't settle. Good luck.

You resent her. It's that simple. When I stopped wanted sex with my ex-wife, it was because I resented her. I disapproved of the things she was doing to me. I was angry at her. Naturally, I didn't want to sleep with her anymore.
If you feel this way about your girlfriend, then the relationship is going downhill. You might as well end it now, then to drag it another 6 months. You know it's bound to end.

When you have small penis, obviously you wont wana have sex that much

When you have a vagina instead of a penis you are inclined to make 'small penis' remarks in others' threads where they have no place... What a douche.