How do I explain to him that I love him? I really just want him to be happy.?

So there is this guy I have dated for 3yrs on and off. Yes we have dated other people after breaking up but I've always been in love with him. He knows I still love him and he says he still loves me. But ever since he left to job Corp he has been different. We aren't together but we still talk. He tells me that he wants me and him to get married and to start a family. Now I don't object to that at all. My question is how do I let him know I wont leave him or hurt him again? Help and please don't judge.