Me 21M gets FOMO everytime my gf 21F goes out with her friends

get so anxious to the fact of when she’s having fun without me I feel like I’m replaceable to the point where I just get upset or scared I will eventually get replaced or thrown to the side, I’m not an exciting person, I don’t drink or anything like that or when I do I’m miserable, I was in a 4 year relationship before my current girlfriend and everytime she went out with her friends her mates would try and get her to hookup with people, and that’s possibly the reason why I am like this? But it’s not even when she goes out clubbing or anything because since we’ve gotten together she doesn’t really do that anymore. I think me having no friends also contributes to the jealousy or envious of her, I love her with my heart, I date to marry I know she’s the one, any advice to help with the anxiety or severe FOMO? Thanks

Any advice or anything would be greatly appreciated, I’m really trying to cope with it but I always seem to get myself in the same position every single time

TL;DR My girlfriend goes out and I get FOMO everytime, basically it,