There's no handbook on how to deal with a situation like this. There is so much I could say to you and it's all played out in my head as I've debated just what I'd say if given the chance.
I never really thought this day would come. I thought it would always be me and him against the world. But now he's with you, so I have only a few things to ask.
I hope you're able to recognize how lucky you are. There is nobody more caring or more thoughtful as he. You won't meet anyone more willing to make it work than him.
So cherish it, because you won't recognize how much you have until it's walking away from you.
I hope you'll grow to love him even a fraction of the amount that I do. I carry six years of loving every part of him. I hope you can find even one thing to love about him, whether it be his heart, his eyes, his drive to be successful, even through the hardships, etc.
I hope you'll never betray him because he will never deserve that kind of pain. Someone as kind as he shouldn't have to experience the pain of betrayal. While he didn't betray me directly and I never betrayed him, I know the pain and that's something I never want for him. I hope you can learn to push him in the ways he needs.
He'll hesitate, he'll want to give up on his path in life, and sometimes he needs to hear the truth out loud whether it's harsh or not. You have to be forceful but not too forceful. He may not want to hear it, but once he does, it makes a difference whether you see it or not. I hope you can learn how to help him in the ways he needs.
I hope you can give him everything I couldn't until it was too late. I struggled and I doubted a lot. And by the time I was ready, he had given up on the idea of us. So communicate with him. He doesn't know how to talk about what's bothering him until it's all boiled up to a breaking point so you have to be aware of what's going on in his world. Show him every day what he means to you.
I can't exactly hope you'll be the one for him considering I wish I was. But if anything, I hope you show him the love and respect he deserves. I may not have been the one for him, but I'll never stop caring for his well-being and I'll definitely never stop loving him. He deserves the best, even if it isn't me.