Why is she so confused and did she even love me?

Here is the situation, I was with my girlfriend for a year and within that year she got pregnant. Well, when she was pregnant I stuck by her side and told her I will be there for her. Well, we had a beautiful baby girl. Well, two months after we had our daughter everything started to go sour. She changed into someone I didnt know, She got her lil tiny figure back and felt good about her self. Well she started to hang out with her old friends, who where never there for her during her pregnancy none of her friends showed up at the hospital. Well they became best friends and stuff, well she started going out, lying and i cought her a few times. She wanted to take a break and so we've been broken up for a month. Well in that short period of time she has found a new guy and hid it from me for a while, I found out and she professed they where just friends, but they talked everyday and txted eachother every 5 minutes. I tried to get her back every way possible haha and it didnt work. So, I tried to trick my self into getting over her by acting like I didnt care about her anymore. its not easy getting over someone when you have to see them pretty much everyday. Well, I found out threw friends she was doing stuff w/ this guy and dating, Well she finally confessed up. I was pissed but, I loved her to much to stay mad at her. Well, I was like look i don't care if you like him or if your dating I just wanna hang out and be with you, because I miss you and spend time with our daughter and as a family. Well, I stayed the night with her for 4 nights straigh and I would listen to her and her new "friend" talk on the phone hell yah it broke my heart but i couldnt do a damn thing about it. I didnt say anything because she would freak the **** out. I told the guy she's playing him but he's puzzy whipped and doesnt believe me and she will deny it and lie to him if i told him. They fight all the time too so it doesnt make since, you left me because we fought but u like him and you guys fight?? I feel pretty used and haha lied to.... i know a lot of girls who are pregnant and none of their boyfriends have stuck around so my ex is pretty lucky, but she doesnt see that.... so WHY AM I STILL TRYING TO GET WITH HER? and how could she move on that fast and like someone and lie to me straight to my face hahahh girls are shitty for real.. so please give me advice on what to do. Most people say, act like you are over here and you dont care about her and her new "friend"..