So I have this friend who has been very questionable lately. He has been very flirty with me lately like rubbing my head all the time and holding my hand and like wanting me to feel his abs and like super flirty but the only thing is he has a girlfriend. Obviously that's the biggest red flag but like he's doing some serious flirting and I mean I don't want to date him I just don't want to manipulate this into what it might not even be. I needed a third party to give me some realness I guess.
In a nutshell, yes he absolutely is! Though I would just be upfront and ask if he's gay/bi. For a lot of people telling others they're gay is too hard, so maybe his flirting is a way to get you to ask so that all he has to say is yes. I had a GF a 19, so if he's the same age as you it's likely he's still questioning.
Tell him he shouldn't be doing these very physical things because he has a girlfriend and you are gay (and thus might fall for him). If he plays dumb, ask him if any straight guy would do what you described to us.