My daughter's in grade 9 so she tells me all kinds of stuff. When a couples relationship is on the rocks and one of them starts flirting with someone else.....this spreads around the school, like wild fire. This news most likely traveled all over the school to his GF and her friends...so he's dealing with the backlash. If he's a guy with decent morals, he probably realized his spontaneous actions weren't good, therefore regrets it. Many teenage boys aren't good communicators, so pretending /ignoring you, is his way of dealing with the social awkwardness of flirting, when he still doesn't have closure with his GF. There's also a lot of game playing too- for example he may have felt its justified to play flirting games with you, since he's bothered by his GF doing what she did...payback.

I agree with Lido - find a guy who's kind and doesn't flirt with every girl he sees. A guys who still has emotional strings to another girl will never be fully yours. I wish I had an older person to coach me when I was younger. Good luck.