serious advice!!

Me and my ex broke up Oct 2015 yet we were still sleeping together i ended up pregnant in July and even before that things were really bad! We fought all the time and the pregnancy made things worse. He told me to get an abortion, I didn't i kept the baby and went through most of my pregnancy alone. Halfway through my second trimester we started talking again and he even came to my appointment with me, but we still fought. He seemed interested in being in his sons life but I don't think he's taking it seriously. He disrespects me all the time, then tells me he loves me it's like a never ending cycle. He has not spent any money towards our son, even if i ask him for help. I have mixed feelings with letting him be involved in his life. I'm scared he will come in and out as he pleases. Somebody please give me some advice I'm 21 & FTM baby will be here in less than a month. Should i let him be there for delivery,? Sign the birth certificate? My family absolutely despises him!