Anxiety of cheating

Over the years every relationship I’ve been in there was some sort of cheating involved and that’s caused me to really be insecure and have trust issues. I recently started dating a guy that seems to really care about me and when I’m with him I feel like the only girl on the planet. However, I see him snapchatting girls which doesn’t bother me that much because he’s explained who they all are. However, whenever I leave from being with him I always feel that he’s going to find someone better and talk to other girls. He has a past of being a “player” so I think that’s what really bothers me because I’d never been with anyone until we started dating. I just would really like some ideas as to how to calm down my anxiety because I think he’s a great guy but I always think I’m not going to be good enough which scares me because I’m already feeling so strongly towards him.