Falling for married best guy friend?

Perhaps it's time to put some distance between the two of you. Stop thinking about all the things that are glorious about this man and start trying to think them about someone else. Your relationship with him is in your own head. You're cultivating the feelings of excitement when you're around him. You're responsible for your behavior around him. Control it until he deploys, then limit communication with him while he's gone and try to develop a relationship with someone else while he's gone.