I really need some advice

Long messed up read but I need some advice before I flip my lid.

My man slept with his ex 2 months before we got together and long story short she's infertile and was on the pill but got pregnant. She called him 5 months later (when we were together - it nearly broke us but we knew our relationship was worth fighting for) saying she's pregnant and the baby is his. After her saying she had been sleeping around he requested a paternity test when baba was born which she was funny about and then asked him to go to midwife appointments etc which he refused because he said he didn't want to build a bond with a baby if it wasn't his. He said he would keep in touch which he was and then she sent him a message forcing him to pay £500 that he owed her from things she bought in the relationship (she kept a list but didn't count what he bought for her) and he paid it out of my bank but then made the decision to make all further communication through a third party because of her other attempts at trying her hardest to fuck with his head.

Fast forward to late last year, his fucking brother left him a voicemail saying he has a baby and turns out his dad had been talking to his ex behind his back basically accepting baby was his even though there was no paternity test. His ex made no attempt to contact my man saying baby is born so he wrote her a letter saying that if she is his, he does not want his daughter growing up without a dad and he wants a paternity test and then to build a relationship with her and assist financially if she was his.

He heard nothing and I've just stupidly gone on her Facebook to check if the little baby is okay and she's sharing shit with quotes about men being shit and wanting nothing to do with their daughters and posts slating me when i am putting my feelings of hatred aside for the best for her child!! He has tried to get in touch and is planning on doing again and again yet shes playing victim - am I wrong for being mad here?! He is a good man and it's affecting his life knowing he might have a baby in this world that he can't see and this situation is making me worry about the impact it is going to have on our son when he arrives!

I forgot to say that she admitted to him when they were together for the short time that she didn't let her other childs dad go onto the birth certificate after he asked because it means she gets more in benefits!!! We can't afford for my man to pay child support but he wants to providing she is his!! She literally said on the phone to him 'You are stuck with me for the next 18 years' after saying that I will never be able to see her (I understand it's hard but she could've at least given me a second to prove that I care about their welfare)