<human>: My girlfriend and I have been together for 4 years and we have been best friends for longer. We've had our share of tribulation but, as far as I know, neither one of us has ever been unfaithful. I am very much in love with her and I honestly don't think she could emotionally handle losing me, so there isn't much chance of this issue breaking us apart unless it escalates to the point where I can't deal with it anymore.  
My girlfriend does not like moving during sex. She prefers to either be in missionary or doggy with little to no movement on her part. I've only ever been with one other girl and she was a freak in bed, and I liked that. I love having sex with my girlfriend, but her lack of willingness to participate is beginning to wedge us apart, causing arguments because I don't want to initiate sex anymore.  
I've talked to her about this a little bit, though not to the extent I am revealing to you nice people, and she replies that sex is not enjoyable for her if she has to ride me or put any effort into it. She says it turns her off but she becomes sort of selfish and doesn't really take the seriousness of my plight into consideration.  
I've been thinking of giving her an ultimatum but I can't even imagine not being with her. We live together on a shared lease and have two cats, so there are also external forces at play here.  
Please, I need advice on this. Or at the very least, to talk about it. Thank you.

Condense the text into a few key points
<bot>: My girlfriend is boring in bed and it is starting to take it's toll on me. She seems unwilling to change but I do **NOT** wish to break up with her.