How is so easy for a man to change his feelings but its so hard for women?

I was recently dealing with this guy that I reconnected with from HS. Anyway, he and I started talking and hanging out when we could and within a month and half, we were inseparable. Im not sure if anyone really understands anything about Chi energy, but our energy was so connected. We felt like time stopped when were together, or the weather was changing when we were together. Me and this guy became emotionally attached. I would find my heart aching for him when he wasn't around,. I got erflies in my stomach whenever we were together. We finally decided to make love and I swear I never felt like that before in my life. ive never had so fantastic before in my life. Recently, me and this guy haven't been speaking much, we used to talk everyday and couldn't wait to see each other, now for the past two weeks, he hasn't returned any of my calls or texts, when I finally spoke to him, he has this whatever attitude like my feelings don't mean anything anymore. Here is the catch to this whole story, Hes married and so am I. Our marriages are not doing well, that's the reason why we started fooling around. im not saying what Im doing is right, but he came at the time when I really needed someone. what do u think is happening? What should I do? I fell for this guy and my heart hurts.. talk to me please.