vaginapagina | need advice

I just found out that I'm pregnant. I want to keep the baby but I don't want to tell the father about it. The reason is that he isn't my boyfriend, he actually is engaged to someone else...I know, it's bad that I slept with him, but that's in the past and I want to make the best of the situation from now on. He does a lot of drugs, he's not a responsible person in my opinion and I don't want him to be involved with my kid. I know he would not be happy to hear I'm pregnant anyway. Can I just refuse to state the father's name? Will there be legal problems or something? Do you think it's ethical to do that or do I have to "give him a chance"?

I don't know, I'm confused right now but my instinct is just to keep him away :(