Relationship help needed

Me and my partner have been together for a few years now. We're currently living together and are very much in love. However recently we've been having a few issues and although we have tried to resolve them someway or another we find ourselves back in the same place and it's causing some friction to our relationship.
I am quite insecure. I have a history of eating disorders and I believe that this is where it stems from. I've never been happy with myself and as a result I question the motives of those around me and to an extent it's on a paranoid level.

The issue at hand is that I am not comfortable with him pleasing himself in a physical way to pictures of other girls...I realise it is a male thing and I do accept that, but it makes me feel inferior. My main issue is that because we live in the same room he either does it whilst i'm asleep (therefore whilst i'm there literally a metre away from him) or when i've dashed out - either way he uses the computer and I always find traces of the sites he has been on.

So he's feeling a little trapped that he can't express himself without me getting upset over it, and I'm feeling completely unattractive as a result of him having to go elsewhere.
I don't have a solution and wondered if anyone could shed some light on the situation. Thanks.