Bad feeling

Hi guys. . My partner and I have been together for a couple of months. In my gut I feel like he is not over his ex wife. I have flat out asked him twice and both times he said there is nothing there anymore. I cannot kick this feeling though. I only found out a week ago that only 8 weeks before we got together he and her 'tried to make things work again' for 3 weeks. It didn't work. But i feel like that doesn't mean he still doesn't have feelings for her.

I mean I am trying so hard to just take his word for it. . But it is seriously going against every grain in my body to just let it go. I am suspicious of everything. It riles me up so much that I question his motives on almost everything he says and does. I feel like I should just leave. I really like him though. I feel like a crazy person now though and I am not EVER like this. . With his answers of 'i don't have feelings for her' I don't know whether I should be questioning him or questioning myself?

Why is this relationship making me feel like an insane person??