Guy i have liked for years tried to kiss me...but he has a girlfriend. what do i do!?

i have liked him for about 6 years now and recently we started hanging out and talking through text messages. i thought it was just friendly interaction until he tried to kiss me. even though i really, reallyyy wanted to kiss him i backed off because i know he has a girlfriend. what do i do if this happens again? i dont know how much self control i will have.