why isnt he interested in sex?

My partner And I have been together a little over a year and expecting a baby. In the beginning our sex life was great, we had sex often. Once I became pregnant it started to slow down and I'm not sure if it's the pregnancy. I can't seem to figure it out. I have brought it up and he says its bc he's tired and I witness him fall asleep on our couch every night by 9 o'clock so I understand that part. I noticed at times he would wake me up in the morning bc he was horny but he even stopped doing that. The other night I told him how I felt and how I always had to INITAITE sex. This time He told me a relationship isn't just about sex. He continued by saying with love comes sex and that He felt that's all I ever wanted so I stayed quiet and didn't say anything. Also, every time we would argue I would try and turn him on which I know sounds bad but for some reason I felt makeup sex worked for us. Until one day... He told me to stop trying to have make up sex bc that's not how you solve problems. He went on by saying he didn't see me as an object and instead of us having sex, we should talk about our problems so ever since then I stopped doing that. Before anyone tells me he's probably cheating or he can be gay, My partner shows me he loves me in different ways. He's the sweetest person ever and I can see he cares about me a lot. Always wants me by his side and is always so thoughtful about me... I'm 33 weeks pregnant and the only position I can handle now is doggy style (sorry TMI) so I wanted to record ourselves and I told him to get my phone. He didn't say no nor did he hesitate. He started to record and within 10 seconds handed the phone over to me and told me to record instead. This was probably about 4 days ago and he's yet to ask for the video nor did he seem interested in it... Just makes me think a lot. What could be the problem? 
Could it be bc I'm pregnant ? 
Could be bc he's almost 35 years old? 
Could it be that he's too tired? 
I know for a fact it's not bc he's not interested in sex. He had a sex video of him and his ex and deleted it after I realized it was still in his computer. This was in the beginning of our relationship. He's always had girls so sex wouldn't be a problem. I just don't know what's the problem with me? I'm 12 years younger than him.