How do I ask my friend out?

Just say it! That's what I did with my partner when we first got together, and we were in the same boat. He was my brother's friend first, but then he started coming over for what I thought was the AC unit in my room but turned out he just wanted to hang out with me. Force yourself to say to him "I wanna hang out together" even though it will absolutely be the most uncomfortable you will ever feel. Doing the scary thing is the only way to make it go away

Just do it! Practice saying hey, I’d like to hang out with you. When are you available? And next v time you see each other, just say it! You got this.