How can I stop being so much insecure?

I think I(22M) am a really insecure guy. Whenever my girlfriend(21F) posts a status of pic with someone else, like standing close to other guy it really boils me up. Ik they are just her college friends but still I hate it so much. And she has a "banaya hua bhai" whom she tied rakhi(he has a gf too) who she spends time with, bcoz their houses are close unlike me who can meet her once in one or 2 months. Yea I really hate that guy. Am I a d!@k for feeling that way? P.s: Our relationship isn't public. Our parents know about us but still she doesn't want to make our relationship public.