Ok, I'm assuming I'm the person who you tried to answer and clear my head, so I'm going to complement your help by "trying" to help answer your problem too.
First of all, "for some reason when he looked at me, his face turned blood red(?).. seemed as if he was trying very hard not to smile"... did this happen right after you "explained your situation to another girl"? I mean, I could be wrong but, he could have turned blood red because he heard what you said to your friend (since he was sitting beside your friend)?
And when your friend told him that you thought he was cute and that really big smile popped out. Umm, I think (with girls too), anyone would be really happy/flattered if someone came up to them and said that they knew someone who thinks that they are cute. But, I guess there could also be something in there too to make the guy smile and show all his teeth and blush like what your friend described.
As for his g/f thing. Umm, well, from what you wrote. It sounds as though you asked him a straight forward question and he gave you a straight forward answer. (Don't know what happened next though).
All I can really say is that he may also like you too, which may have made him blush? (People can't really control their feelings for other people, even if they are in a relationsip already).
But then again, I could be completely wrong since, I'm not exactly problem free at the moment too and my mind may not have analized things properly. -__-".
...Just trying to help.
