Been struggling with this for 5 years

I would just like to know what you ladies would do in my situation. Please no negativity, I just dont know what is the right thing to do. I have a 5 1/2 year old from a past relationship. I broke up with him while I was two months pregnant due to being verbally abused, his anger, his drug use and drinking. There were hardly any good days with him, it was rare. Now we still didn't have a good standing while I was pregnant either and I was always stressed. My doctor told me to stop talking to him for the time being while I was pregnant because it was causing stress which was causing me to have high blood pressure and I went into preterm labor at 30 weeks (they were able to stop my labor thank god). So I stop talking to him and he was furious but my health did get better. Later on I had my baby and I let him come to the hospital to come see our son. He got mad at my nurse and started freaking out in the hallway because she told him he couldn't take the baby right now. They almost had to call security but he left. That was the last time I've seen him. He texted me a few times with in six weeks but I was honestly was afraid of him at the time (plus hormones, I was a mess) so I never answered his text. The last text he sent was that he was going to get a DNA test. After that I've never heard from him again. Now these past 5.5 years I've been struggling on whether or not to contact him to make him a part of my sons life. I feel as though it's not fair to my son that he gets an absent father but on the other hand I have no idea the type of person he is now. I dont want my son around an angry verbally abusive man who uses drugs. I would gladly put my hatred towards him aside if it ment my son gets to have a good daddy. Now a few months ago his now gf (soon to have a baby) messaged me on Facebook saying I need to let him be a dad and I am hurting my son by keeping him away. I've never once told him he couldn't be in my sons life. He has never taken me to court, came to my work or my home (I lived and worked him in same place for 7 years), nothing. I feel that if he truly wanted to be there HE would do something and talk to me, not his gf. I am split down the middle on what to do. I just want my son happy and safe and he is right now with me. I'm afraid to make the leap and it turn out horribly wrong. My son has got dealt a shitty hand and he is an amazing little boy and deserves so much more then what he has got. What would you do?