How do i know if my friend is gay or by! and does he like me?

Okay, so. I am a guy, 18 years old bisexual (kind of more attracted to boys than girls and started college this year. I am straight acting and nobody knows that i like men. I have had this male friend for around 2 years, but I have known him for about 8 years, because we went to the same school. We are not really close friends but we talk to each other, and we are also in college togheter, we go to the same classes and I spend a lot of time with him. I have had a crush on him that started like 3 and a half years ago. He is supposed to be straigh, he got a girlfriend last year, and they have been together since then, she is also in college and we go to the same classes, she is also my friend.

I really have a huge crush on him, and sometimes I doubt about his sexual orientation. Last year we were sitting in the back of a car, we sat down at the same time and for some reason, his hand ended up under my ass, I just know that I was sitting in his hand, and he didnt take it out during the whole ride...I mean, he must have enjoyed it or something, because if you are straight, you woud have taken out your hand like in two seconds, but he left his hand under my butt like for 10 minutes until the ride stopped. All the people in the car were talking and we had a normal ride, and me and him never talked about it.
He is also very nice to me, he smiles a lot to me, and sometimes we have some weird eye contact. Or if we are sitting close, owr legs touch warch other, or owr feet touch too like in a weird way. Somethimes he also speaks like a little in a gay way. I have to say that he is like the hottest guy I have ever seen in my like, I am like obsessed with him. I think that I am starting to fall in love with him. I have even masturbated watching pictures of him ( normal photos).

HOW CAN I KNOW IF HE IS STRAIGHT OR NOT? I know that he has a girlfriend, but for some reason i think that they made all that up, and that she is lesbian and thay are doing it to cover up their sexual orientations ( like, they became really good friends, and one day they found out that they were gay, he gay and she lesbian, so they came up with the idea of faking a relationship to avoid other people finding out about it in the future) , or he is just having her to hide that he likes men ( using her, many gay guys have done that to avoid people suspecting about the true). I say that because I have never seen them kiss each other, only like hugging and small cheek kisses. She also dresses in a not so girly way, kind of like a lesbian, not extremely, but like in really serious and boring way. She also had a drastic haircut before starting college, from a long hairstyle, to a short hairstyle.

Once we were all having lunch togheter and with a few more friends and he was talking, he started talking like in a gay way (not extremely) and after a while, she told him like "Hey dear! You are being so gay today!" I mean, are they really faking up their relationship, and she was telling him like trying to say (hey, watch out! You are talking gayer than usual, moderate your self or they can suspect something....)

So I just want to say, I really like him, how can i tell if he is gay or not? And if he likes me?. i mean...the way he looks at me and that butt touch... And do they really are faking they relationship, or he is just using her? Or it is all in my head? Im really confused, and dont know.....,what to do?. i would like to talk to him about it but i dont want to mess up our relationship. ( and maybe was he waiting for me to do something in reply to his butt touch, but he stopped trying to reach me sexually cuz i never talked with him or did somethin about it,). Should i do something a little bit gay, to see how he reacts?

Well thank you so much if you are reading this, really apreciate your time and opinions! Im really desperated about it.
David.