sexually conflicted

so my ex and i broke up and during that time he dated someone else and i did too. i started to like this guy and then we broke up. after we broke up my ex and i got back together. we’re doing good everywhere else except the bed. he doesn’t have any problems but i do. i cant get off with him and we tried a lot of different things. even toys, if i do get off i have to imagine it’s the other guy i dated and it makes me feel terrible. even when masterbating i have to picture and think of him or i cant get off. i don’t know what to do. some of my friends are saying maybe i don’t love him anymore and i’m forcing it and some say it happened to them before. can anyone help here i feel stuck