This is a long one but need opinions!

Okay, so I need some advice if you think this is wrong of me or not… I am almost 17 weeks pregnant, I found out on June 9th and when I told the father he said he wanted nothing to do with the baby. I hear from a coworker  (the baby’s father used to work in our building but no longer does) just a couple of days ago, that she was talking to another person in our office about how he and I were dating. The other person was like “I didn’t know Sam was dating, I thought he was like engaged or married.” So, this brought back a bunch of feelings for me because early in our relationship on two separate occasions I asked him if we was engaged because I’d been hearing rumors. He denied it and I trusted him. Well after I heard this I got curious and did some investigating. I found the supposed fiancés Facebook page and she is in fact engaged, or at least still with him, and they just had a baby together on May 31st.  I looked back at my texts and he was texting me that day asking me for nudes. He was at my house on june 3rd having sex with me.This hurt me on every level. Not only is he denying my baby a father while he fathers someone else, he lied to me time after time, he lied to her time after time, he used me. He knew exactly what he was doing and I’m disgusted by him. It's an anger and hurt that I've never felt before and it makes me sick to my stomach. 

 Anyways, the reason I am posting this is because I am going to tell her. She needs to know. However, I’m struggling with when I should tell her. I’m due Dec 24th, and I will be filing for child support (he has already agreed to pay) and I know it can take a couple months for it to be finalized. At the time of our court date for child support they will go over visitation and if he wants to sign away rights, etc. I want to tell her now because she deserves it, but I also want to cover my butt. I don’t know her and my worst nightmare is that I tell her before we have our legalities worked out and she breaks up with him and then since he no longer has anything to hide, he will want to have some sort of custody. If that happens and say they get back together, or they’re together because they have a child together as well, while they have my baby, what if she does something? She could hate me and be angry and do something to my baby. Or what about his family? I don’t know any of them, what if they do something while the baby is with him. I have no concerns with him harming the baby, I know that much about him. And he is a police officer, he takes his job very seriously, so I know he wouldn’t do anything to jeprodize that. My question is, is it wrong of me to be silent for the next 6ish months knowing and not telling her? I do plan to tell her of course, I just don’t want any issues and I want to have by butt covered. Obviously this all may never happen, it could go the opposite, but I don’t want to risk it. Also, I am going to counseling to talk to a professional but that's not for almost 2 weeks. Please help!