He mimics your body language. When people are listening to one another intently, they tend to subconsciously imitate each other’s body language. The next time you’re engaged in a good conversation or discussion, cross your arms, put a hand under your chin, lean forward, take a drink from your glass, etc. If he tends to follow suit, it means he’s very focused on you.
He smiles and sustains eye contact. Platonic guy friends smile at each other. They also make plenty of eye contact. But if your guy makes prolonged eye contact while flashing you a big grin, he’s being far more intimate than most straight guys are around each other.
He wants to know all about you. Guys aren’t known for their ability (or desire) to untangle the threads of their guy friends’ personal lives. If your guy asks a lot of questions about your life, interests, hobbies, friends, and, most importantly, feelings, he isn’t content with chitchat and wants to get to know you on a deeper level. Or, you're his best friend.
He touches you unnecessarily. Straight guys may hi-five, roughhouse, or even slap each other’s butts on the playing field, but most won’t feel comfortable with touches that aren’t rooted in play. If your guy lets his hand brush against yours, puts his hands on your shoulders while standing behind you, gives frequent hugs, or finds an excuse to pull something of your hair, he’s probably trying to kick the intimacy up a notch – or even test how you react to his advances