My ex fiance is taking me to court for full custody of or three year old. im not a bad parent nor person?

we have been together for 7 years four 4.5 years engaged. well i decided that we needed to separate because he was just getting to the point were he was just still taking me for granted and going out with friends and alcohol started to become a issue. it was always a concern of mine but iv looked at it like oh well he will grow up. but its not about that now. so in like august i started to talk to this guy and i told him about it, and he flipped. it wasnt nothing big just talked. and so in the month that we talked and hung out, my ex fiance was just the mean evil and saying im a bad mom because i walked out on them because i tried moving on with my life because he obviously wasnt going to change. so month and a half went on and then he just beat me down with negetivity and hurt thinking i was doing a bad job as a parent. which i was not, i was always there for them night or day, our agreement was he would get them on Thurs and they would come home on Sundays. so i would call and check on them all the time. in the mean time he was always like well we need to get back together and how much he loved me and he was going to do this and that. so like a sucker i believe him and ended the relationship with the new bf. and in the mean time in august my father had ped unexspected which i was already hurting, and dealing wiht his meaness and selfish ways. and so like i said i said i would like it if we were together, so i thought that we were. well then it was oct 9th, and i was out of town because my grandma was i the hopsital and he had the boys. and she was not doing good with cancer, well he calls me at like 6pm and says that his brother and his wife are getting the big d. because he caught her texting another man again. so he said that he wanted to go the local bar and have a drink with him....so i said okay as long as your home before 1130pm and he said oh yeah thats plenty of time. i found out that he didnt come home till after 430am and he was with his brother and his wife and her causin at a different local bar(and he was on a date) how cly!! and my grandma is laying next to me fighting for her life and he pulls this **** on me! So i was crushed dealing with that and my grandma who i was very close with. well that sunday she was sent home on hospice, and died two weeks later and that night he said he just had to go to work at a different town by 5am and couldnt keep our son, so i left to go get him while she was dying and i drove there and he was texting his new gf on my cell phone and our son wasnt ready and he was running all over. so told him i wanted my cell now and he didnt give it to me and started yeilling saying i made him do this ..having a girlfriend and move on. when i was like what i thought that we were together and he said ohh no. now that he has a girlfriend and i found out. but he ended up hitting me , scrapped and bloodied up my knee and pushed me into our gl patio door and i was in major pain. then he just ran out and went to his dads and i called 911. but with this all said and done. my gma died 40 mintues ago. and the police came and he denied everything. but he has been so mean and evil since he has this new girlfriend and im just like this is to hard very hard.