Support, advice on placing for adoption

I’m currently 6 months pregnant. I have been on the fence about giving my son up for adoption since I found out but in the most recent weeks I have been more for doing adoption. But at the same time I feel like I am being heartless. I have three other boys and this pregnancy was not planned in anyway. I don’t talk to the father. Him and I broke up three weeks before I found out I was pregnant I have talked to him twice since finding out that I was pregnant and I don’t know what to do. I want my son to have a happy, healthy life with a family that is going to love him and give him everything that he needs. But I’m also afraid that if I sign my rights over and he goes with his dad he’s going to end up in the system at some point. His father is irresponsible, doesn’t have a job or car or stable place to live, and he’s always out partying and smoking and stuff. Now I know that no reason to think that he’s not a good father fit. Is there a way to do adoption without dad being there or knowing about it? Am I in the wrong for wanting him to go to someone that with love him and give him everything he needs? Am I in the wrong for not wanting him to go with his dad who in the end will not be able to full care for him?

I feel like the world’s worst mother for even wanting to do this but I am not in a place right now where I can care for a 4th human being or full support him. I want him to have the best life he can in a place where his family isn’t struggling.