How should I feel about him?

I dont know why but I feel really heartbroken but I dont understand why this guy started liking me late last year at school and I never had the guts to talk to him around may I finally did talk to him he surprised that I talked him I guess. He knew I liked him and he knows I knew he liked me. When we would see each other we’d always say somethingthis last friday that passed I saw him again he saw me too but he went the other way with his friend said something to his friend something about me and he made me feel soo bad soo stupid at the same time because I had been looking for him and when I finally saw him he left and today I saw him with this girl I guess she ‘s his girlfriend. Everything was okay until friday happened. I just dont get it why would he sort of do that you know he also doesnt really let me see him. Is it because he doesnt want me to see him with that girl? And I feel betrayed in a way. What does a guy notice in a girl usually? What do guys ike to talk about with girls?