Please. You are fantasizing about this guy. He's married. The fact you were his student makes no difference. Students get crushes on their professors ALL the time, its about the power of the position.
Why are you posting about "even if he left his wife" unless you are thinking about it? The apology thing is just an excuse to contact him. I guarantee he is perfectly fine living without your apology. I doubt he's wondering every day "Why hasn't she apologized yet??"
Find some single guy to throw yourself at. Not a married man. Geeze, have some self-respect.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh