[B/S] Brother got an erection

So I am 19 and live at home. He is 22 and goes to a university. He came home last Saturday for Thanksgiving break and things have been pretty normal. Last night we watched a movie as a family and I sat on the couch with him. I was leaning against him while watching the movie and I noticed the lump in his pants. He sat like a statue and seemed uncomfortable, but I didn't want to move and draw attention to it. Our parents were in the room as well.

He leaves back for school on Sunday and I don't want to miss my chance. I am not super confident though that he wants the same thing I do. How do I tell for sure and how should I approach him?

Edit: Okay, so I realize I didn't put a lot to go on. We've always been close until he went to college. Buy when he comes home, it's no different from when he left.

Something you may need to know: I'm a hugger. Always have been. I hug strangers when we meet. I hold hands with my friends a lot when we go out. It's not sexual, just what I do. So me leaning on him when watching a movie is not unusual. I need something to show him I'm interested instead of me just being me. Or someway to talk with him about it without being obvious.