I can’t let go of the past

I been with my bf for over a year. In the beginning we were talking at my old job we were like best friends. I always wanted to be with him and we were both in shitty relationships. He was getting cheated on and so was I but his case was worse because he lived with the girl. Well we started talking more and more and things ended not so good with her and they left each other a few months after I broke up with my ex. After they broke up, he was constantly checking her fb multiple times a day and she was even begging him back behind my back. ( we were dating ) I of course didn’t know but I found out and was hurt completely that he was still showing interest in her. He started dating me 2 months after they broke up because I wanted him to not be with me the next day. He hurt me in the beginning and she use to bother us every now and then and he’d tell me whenever she tried to talk to him. Now she’s long gone and has a new man and left us alone and pregnant and all. But I mention her sometimes because I get scared of getting hurt and it’s been over a year and I dont know how to let it go honestly... I just want to know he’s over her because they practically had everything together. An apartment, bank, phone... Advice please? I wish I could let it all go.