Should I tell him or should I wait?

okay I like this guy who I’ve known for 8 months and we’ve gotten close since we have 2 classes together this semester…I think he likes me back because he touches me(arm, thigh), teases me, jokes around with me, compliments me on my clothing, stares at me, randomly looks at me, he asks me what’s wrong when I’m sad, he stares at me when I walk pass him with my friends etc. but he also talks to this girl in our class, they are pretty close too but they don’t flirt around like we do but yesterday they spent two periods together with friends, and they talk for the whole period everyday and I think she likes him but she has a boyfriend…nowadays, he barely says anything to me in class and whenever he does, she’s always interrupting me…I think she likes him because everything I do to him while flirting, she does the same exact thing. I just want to tell him how I feel because I’m scared that he’s gonna start liking her, I can feel it…that’s how we got close…or do you think I should wait?