Girlfriend (18F) lets other guys flirt with her when im (19M) not there?

So my girlfriend (18F) has this friend group with some guys in there. Two of these guys has a crush on her and have been chasing her for quite a while now. They both are considerably richer than me, but im pretty well off and they give her everything. I’m not really insecure about myself, if she thinks they’re better than me im the type to let her go and not really put the blame on myself. These guys offer to drive her places, pick her up, buy her things, and she often lets them do it. For example today he dropped her off at a restaurant for our date and she didnt mind telling him that she was going to meet me. He also wanted to go out with her and she said no she had somewhere to go (with me but she didnt tell me). He then held her hand and like shaked it asking her to go and she let it happened. This flirting has happened for quite a while now and she said she ignores them but they keep flirting til now and its still pretty bad even after we started dating. Does this mean that shes letting it happen and is enjoying their flirting and attention? One guy also said he doesnt care about her having me as a boyfriend and that its not a problem for him and he will continue to chase. However, there are certain times where she doesnt go with them because shes afraid it’ll make me feel bad and does always choose me over them. What should I do?