Am I overthinking this?

Question

Am I overthinking this?

I been dating her 3 months and we just graduated. She has a lot of hs guy friends but rarely hangs out with them (once a month). There's a particular guy friend of hers that has been bothering my mind for a minute. She likes this guy's pics/post on facebook a lot and if he posts a joke she will put lol hahahah. The things he posts aren't just posts some say "i need a girl who's real and knows what she wants", "i kind of want a babe and kind of don't". Another time he told my girlfriend "you a real one" and my girlfriend replied "real recognizes real". If this isn't enough my girlfriend last time told him "hey we should race with our cars one time and drink a beer after". Three months later after i read this she was wishing dude a birthday and she said "Happy bday and her don't forget about our future race" something like that she wrote but she indeed reminded him.

Am i being jealous/overthinking this or is this girl on the way to cheating? no she doesn't txt/call him or hang out with this guy he's just an old classmate of hers and to be honest he is a threat/competition.