SUBREDDIT: r/relationship_advice
TITLE: [21/M] My girfriend [21/f] is her friend's date to their friend's party.
POST: My girlfriend of three months has a friend that I reckon has a crush on her. He always offers her to drive her around, to study together. Just recently he asked her how long we've been dating, if there's any problems in our relationship (arguing, etc).    

They have a mutual friend's birthday coming up, and he wants to go together with her (she was invited as well). He went as far as telling her not to wear heels (so they'd be the same height).   

His aggressive approach is making me slightly uncomfortable. However, my girlfriend just sees him as a friend.    

Should I just let it be? Should I be jealous? Should I tell my girlfriend? Or should I talk to this guy face to face?
TL;DR: 
A guy has crush on my GF. He is taking her as a date to their friends birthday. Not sure how to react, if at all.