Nervous of a idea that could change my life

So my boyfriend and i have dated for a year and four months, were highschool sweethearts and i love him. But i am very nervous, we moved in with each other into my condo after highshool , close to my university, 45 mins away from our hometown. I caught him a week after our 1 year anniversary talking to a mutual friend (girl) about hooking up and that id be okay wth it (also he told her in another convo that she isnt fat and mentioned my weight which is 200lbs) and so i was totally distaught and my trust completley shattered there. He has before told me he was losing passion with me and ge also told me (in highschool) after a 3-4 day field trip that he was thinkig of cheating but didnt..my emotions and gut get sick everytime i think he may be talking to someone. He moved out fter i gave him a choice between me and another girl he was talking to online (he says thy were just friends) but he couldnt give her up. After being a month apart and i went out on dates i could only think of him and he was the same. we got back together and i am scared that if i move back home and he moves in with me it may be like this again. I dont want to be heart broken again and im so scared, advice?