idk what im doing :(

I've been in a relationship for a short time, it's my first relationship. I guess because I never really thought about it and because it's obviously my first relationship, I feel like I'm not doing so well. my girlfriend has had other relationships, I even know some of her exes and I even feel a little out of place sometimes :( this makes me question if I'm really on the right path for this to work, honestly I don't know what I'm doing. sometimes , her best friend (whom I adore, by the way) comments on the people my girlfriend has kissed and talks about her experiences and before that was fine for me, but nowadays it bothers me a little, I think I don't want to imagine my life anymore girlfriend with other people, it's a little torturous and I'm not as mature for it as I thought I would be