Here is my take on it. You need some more self esteem. He's shopping for rings for you, not his friends girlfriend. Who cares if she's hot? There are a lot of hot girls out there, that's the truth. In my opinion you totally opened the door for his comment about the other girl. #1 He's pissed to begin with, #2 He's probably giving a detailed explanation because the conversation started on the premis the friend was gay so he was attempting to inform you of the g/f, #3 Talking about the friend isn't gonna make him any more pleased.
You in my opinion probably read WAY to much into what he was saying. Are you sure it wasn't Yeah! (amazingly enough she's hot) or Yeah! (don't know why she's with that guy?)
So then after making him feel bad, when he's already pissed you blow it out of proportion at the resturant, probably making him feel worse, so he gets mad at you. Not saying it's the right thing for him to do, but probably what happend.
Then since he's got the serious jitters about getting married and the future and all that stuff (like most guys), so he see's a convienent way to buy some more time. IE Spaz out and create a situation that creates confusion. (When he insisted on staying at a homeless shelter) In this case, it's a clear showing of his IQ when angry. (not getting any scholarships there)
I definately agree you had a legitimate point with walking back alone. For that, he deserves an extreme *** kicking. (Like what the Vikings are going to do to the Packers tomorrow) Okay, even worse than that. I'm actually serious about that. I can also see his point in that matter. You didn't back off, so what was his choice? How does he "win" that battle? The answer is simple, the guy doesn't because the girl he cares about is WAY WAY WAY more important than the idea of winning a fight.
Nor for my relationship diagnostic.
He's too probably too old for you. 8 years generally seperates all your goals and desires. Since you are 20, I'm presuming you have an additional 2 or 3 years left of college to attend. Having somebody in college, living away from you is a very hard thing. It's definately my opinion that it's not the correct situation to be working on marriage. It's your call though. My mom and dad are 8 years apart. It's a huge difference in the way they see things sometimes. I'm not involved in your relationship, but don't hang onto it just because it is a relationship. If you two are serious, and you do love each other, then great. If not, don't make it a "worlds ending" scenerio.
I hope my response isn't too harsh, I'm not trying to make it that way. Just the way I see things.
Good luck in any case, and keep your head up!
Kell