I think my brother is in a secret abusive relationship

My brother goes to university out of state so we don't see him often, but when we do see him he has obvious peer-inflicted bruises and is always trying to hide who he is texting or talking to on the phone. He seems constantly nervous and gets really defensive over his phone, his general spirit seems broken. He was always so happy-go-lucky before University.

He's very smart, but he's always been a pushover and a very charitable guy. My mom and I have had our suspicions that he might be gay for a while now, but he's so outdoorsy and makes it into a joke if we ever subtly hint at the idea.

His wrists and neck are often bruised when he comes over, but heal while he stays here, he's also shown up with a self-sewn stitches in his cheek and black eyes before. He always has an excuse or a story as to how they happen. He refuses to take his shirt off, even when we go to the beach so I don't know what other injuries he might have, he's always been very outgoing until now.

He isn't on drugs, my mom has drug tested him multiple times. I just want my brother back.