Can my ex boyfriend of 2 years really get over me that fast and start dating a week later?

So i had been dating my ex boyfriend, for about 2 years. I have known him for 5 years, and I have had him as a best friend since i had met him. We got along so well, as if we were soulmates. After about a year and a half, things were starting to get way to serious, and we were both so young (18) he thought it would be a good idea to break up, and see if being together was really what we wanted. In other words, he wanted BOTH of us including myself to get out there and re-ure our feelings for one another, by overcoming obstacles, like meeting new people. At the time he brought that up, I was really into the relationship, breaking up was the last thing on my mind. He insisted, so i accepted. We were both in our own little bubble for those two years, only being with each other, since he never really let me hang out with my girlfriends. We were both pretty jealous. During about two weeks, he met a lot of people ( a specific crowd of guys who werent the best influence, street bike riders to be exact. ) As for me, I was stuck at home not wanting to do anything, or meet anyone, since all i wanted was to be with him. Although we didnt lose contact, after about two weeks i realized it wasnt so bad being single sinceI realized i had put aside so many of my friends.Then i decided to throw a huge party, and since i was single again, tons of people were expected to come, since i was pretty well known. One day, over the fone he asked me if i was really having a party. And although i didnt think him coming was the greatest i dea, i told him it would be okay if he came. That night, he brought all of his friends, and he was pretty much in shock when he saw how packed my house was, and how fast i got back out there. He followed me around all night, i acted completely careless, since it was my time now. He introduced his friends to me, and once guy in specific caught my attention right away, and i caught his too. This guy was pretty much the hottest guy in their crew, so this threw off my ex. That guy asked my ex if it would be okay if he got my number, and my ex acted like he didnt care, so after me being with the guy (my ex's friend) almost all night i realized i kinda liked him. After everyone left, my ex still kept calling me trying to talk. Next day, the guy i met asked me to go out on a ride, so did my ex. But i went with the other guy instead.Basically, to cut it short, i chose to be seen with my ex's friend, instead of my ex. My ex boyfriend begged me like crazy and i was too busy hanging out with his friend. (who is knows as a player btw) One night in specific i lied to my ex by telling him i ,wasnt going out, when really i was gunna be with his friend. He showed up at the same place, and saw his friend and i hugging, and acting like a couple. After about a week, i made up my mind, and realized i really did love my ex. So we went back out. His friend took it just fine. we dated for about 6 months after that. It was hell, since he never treated me the same. He wasnt sweet anymore, he was cold, and he always brought up how bad i crushed him and stepped on his pride. He then decided he couldnt take it anymore, and he brokeup with me. I was crushed, and shattered since i truly love this guy. We stopped talking a week ago, and i just found out he's dating a girl, with a three year old kid. He met this chick a day before he broke up with me.They havent made the relationship public, but heknows that i know. How is thispossible?! could he really have gotten over me that fast? he knows exactly what im going through and he's simply heartless. Its crazy to think that one day a person is ur world, the next, they dont even exist. Help!