If it was your own son what would you expect from him? To obey you or to disobey you? How about your parents? Do they agree? If they do, can they go ask for the proposal? They have a better shot at it than you both trying on your own. If your parents disagree as well, then it sounds like a seriously uphill battle.
Remember, you know him for a few moments for just 3 years and possible never sacrificed for him. His parents and his family have RAISED and Sacrificed for him to where and what he is today.
This is indeed a timeless issue and a very serious one. You have already known him for 3 years and unsure what the depth of your relationship was but the best thing to do at this time is pray that Allah forgive you and us all for our sins that we did knowingly and that we did unknowingly.
There is no problem in approaching the family through proper channels. The fitnah comes in when you both meet and continue this relationship. Whoever your mahram or wali is, they will definitely do what is best for you but you just have to pray and have faith. And Allah knows best...