Boyfriend wishes he was having sex with his ex

A couple months back I used my boyfriend's phone to locate mine. When I opened the phone I discovered that he typed in Google that he was dealing with managing his attraction to his ex. I confronted my boyfriend about it and he revealed to me that he went on his ex's Instagram twice page and each time in the moment of looking through her page he was wishing he could f*** her and was reliving having sex with her. I was very hurt and I cried about it. His ex was abusive so it makes the whole fact that he's still obsessed with her even more traumatizing for me. We have been together for 2 years and 2 months.I understand if she was a good person at least but I personally would never be caught up about wanting to have sex with someone again who was so abusive to me like she was to him. I suggested that he go to therapy to fix this trauma Bond. He's gon to a couple sessions of therapy but can't afford the rest so it's been a bit of a hiatus moment. However he has books to read about trauma bonding but it seems like he's has stopped reading them. I feel very upset about this because it shows that he doesn't take my pain seriously. I get that he can't afford therapy right now but at least if he was reading the books to help get over this feeling of his. We were making plans for marriage which I've put on hold because he's still obsessed with his ex. If he was consistent with trying to get over his ex iI would feel a lot more better. My questions to you men is that is this something that a man can ever really get over? No longer looking up their ex and wishing they were having sex with them when they see their pictures? I don't expect him to never think of her every now and than or never have a sex fantasy. But the obsession of her? Or should I just cut my losses?