I'm hoping for a little perspective on this as I have limited experience having only had two sexual partners.
I have been with my boyfriend for eighteen months now, we live together and all is mostly good. We laugh together, spend lots of time together and he is kind and thoughtful.
My issue is that's it's nearly always me that has to instigate sex and when I do he thinks nothing of turning me down. When we do have sex it is amazing. I feel like he's not that bothered and would just as easily go to sleep though and it's really starting to get me down. I have spoken to him about this and he insists that this is not the case but again I'm lying here feeling rubbish while he sleeps. I did instigate last night but got the response 'can we have sex tomorrow instead' 
Does anyone else have the same problem? How often do you have sex in your relationship?