It's awesome to hear self-discovery stories; they make me all warm inside.
Anyway, pretty much what Marcus said. Honest and open communication, respect, patience, etc. He might not stick around, and that's a possibility you should probably put some thought into preparing yourself for. Coming out poly is rarely easy, especially in your situation, and I wish you the best of luck. May things go your way in the future.
Me: Straight male, anarchistic polyamorist, hate labels
N: Straight male, best friend throughout childhood
M: Bisexual female, introduced her to poly
C: Bisexual female, 'girlfriend' of N before poly encouraged de-labeling
A: Straight female, newest in my life
I love them all.