Dude, I don't want to seem trite but this is no big brainer.

You guys have sexual history together.

You are both obviously still interested as some level.

So the trick is .... keep away from situations where you will have opportunity to give in to temptation. Ie: don't be alone together.

If you regret what happened, I suggest you tell your friend that and put some boundaries in place so it don't happen again. Take it to God and confess and repent.... then put it behind you and move on boy.

Learn from this.
You are a sexually vulnerable young person. Have your friends... but keep away from spending time alone with guys you are attracted to.

Bless ya little brother.
Cat.