There could be one of many reasons such as he is scared, not ready for such a commitment, changed his mind, taking some time to think - but he is the only one who knows for sure why he has done this. Give him some time and space, don't pressure or pester him concerning this, allow him to come to you when he is ready as he may just need some thinking time - this is a big step for a man allow them breathing room.
The same way you would break up with any other guy! Age is just a number.
They are still going out - they have been for 18 months. He apparently proposed to her before she arrived at Brown University as he was afraid she would meet another guy.
wait for them to break up ( if they do).
Well, if the guy liked you that much he would break up with his girlfriend. But by the looks of this you are coming up as second best.
If the guy really loves you there is no way to break up with him without hurting his feelings....
If he "loved" you more he would break up with his girlfriend to be with you.
You would need to ask the guy.
Yes, because she wont give him what he wants.
the same way you break up with any other boy its not like they are aliens and dont react the way any other dude will so just break up with him like you would with a normal guy.
Embarrassment.
He wants to break up with you and has no good break up lines.
To break up with a guy who is your best friend do this. Talk to him about the matter. Tell him the reason and stop talking to him.