My brother's roommate won't get closer to me because of my brother; what do I do?

I went with he and my brother to a concert and my brother ran off on his own leaving us to hang out. We had a fun time and he definitely has feelings for me. He's not my brother's exclusive roommate. They're fraternity brothers but they are somewhat close. My brother knows how he feels and is indifferent about it. How can I convince this guy that my brother wouldn't be a factor?