It all depends on you. You need to think of yourself right now, not how your mom is going to feel or anybody else for that matter. Everybody has a right to know where they came from. Meet one on one in public, go for coffee see how you feel. What kind of vibe you get....then go from there
I see the dilemma. Meet with him and have coffee to find out why. Maybe he has been racked with guilt and is now emotionally in a place to have a relationship with you. He might have been away for good reason. He might have grown into the kind of person you would like. He has to be ready to hear what it was like to not have a father, so he needs to be solid enough for this, but not at the first meeting. Or, he might be checking you out to see if you can give him some money. Who knows? But if you don't meet with him, you will never know. If it's money, kick him to the curb. If he wants dialogue, let him speak without blowing up. It could lead to something really wonderful in your life. Get to the coffee shop early, pick your table and watch him arrive. Keep an open mind. Ex-spouses get bad-mouthed a lot and aren't there to defend themselves. You've only heard one side. If he was addicted--it might be done. If he was too young--well, he's older now.
Your question is gutwrenching because something similar happened in my family. My brother got another woman pregnant while he was engaged. The fiancee said she would still marry him if he had nothing to do with the child. My brother was an 18 year old drug addict at the time. He attempted to connect with the daughter when she was 18. It was lukewarm and now he just follows her on Facebook so he doesn't interfere with her life. Well, guess what? I'm still missing a niece and her kids. There is a hole in our family, someone is missing. Possibly, you are that someone in your dad's family. You may have family that has always missed you and prayed to meet you someday. Please give your dad and them a chance!