Having marriage problems. Really don't know what to do.

Will try to keep this short but there is a lot going on. Firstly, I have a brain injury that has affected my memory so am never quite sure if I've forgotten or am getting muddled which makes things very difficult when I try to discuss things with my OH. My problem is this, I think my OH still has feelings for his ex. There's been many things that make me thinnk this, he defends her if anyone says something even slightly negative even though she cheated on him. He once said, straight out, that she was much prettier than me (still hurts) He often made remarks about how thin I was and that I needed to put some weight on, the ex is quite large. He once said he had been discussing my medical conditions with her and I blew up about it and said he shouldn't have done that but he said she had a right to know as it might affect his kids (it really won't as I have barely any relationship with them) The thing is, I don't really understand if I'm worrying about nothing as I don't seem to understand things so well anymore or if there is a problem, then what do I do? I have tried to talk to him but it doesn't seem to come out roght as I get flustered and then he gets snappy and I just drop it. Any thoughts?