2 Babies in one year...BM drama

So I started dating my bf early February of this year (2019) and we’ve been great since. I’m currently 8 months pregnant with our daughter and we’ve discussed getting married within the next year, so we’re very serious about each other. Coming into the relationship I knew he had an infant son but he had cut things off with the mother before she even found out she was pregnant. She had their son on Jan 24 2019. Well, Nov 29 2019 she messaged me on FB telling me to have my bf call her bc she “had the baby” and I just saw the message today on Dec 3. I am so confused bc I had no idea she was pregnant and my bf says he didn’t either. However she has a few FB posts that seem to imply he’s the father of both babies and I’m honestly so blindsided right now. I don’t want to believe he could do that but my last relationship was so toxic and I learned people can and will do anything regardless of someone else’s feelings. Is it wrong for me to be paranoid? And is it possible she’s trying to get in my head to break us up (I know she still wants him bc she said it on her FB as well)? My mind is racing and I’m trying to stay calm but I don’t want to end up heartbroken again. I feel stupid for falling so quickly for someone. 😔 am I overthinking?

Edit: they coparent so I know he’s seen her. I asked about that and he said he didn’t notice anything bc she’s on the heavier side anyway and she always wore loose/big clothes. He was kinda acting like he didn’t want to discuss it too which makes me even more paranoid. He said he would talk to her about it tomorrow but I’m wide awake now bc I can’t stop worrying...I’ll bring up a paternity test but I’m honestly so scared of the results. Even if it was before me, he said they were done by then so I’d still be kind of hurt but I could handle that a lot better. I’m so confused bc he is so genuine and all of his friends and family tell me how he’s a good guy and he loves me a lot (I know he does bc he’s been to every appointment and stuck with me through so many breakdowns). I feel so bad for doubting him :/

Edit #2: so her due date was dec 15...wouldn’t that mean conception was in March?

Edit #3: okay, so we talked yesterday and apparently she straight up said it isn’t his baby which makes sense bc we were dating at the time and i think she had a guy staying with her at the time on and off. I’m relieved but this still complicates things bc the dad is a drug dealer who got her apartment raided with her first son there to witness so that’s just great. I think she was just being petty on FB but I can get over that (she’s getting blocked lmao). I’m just glad it’s all sorted out. Thank you guys so much, though, you all really helped at a time where I was lost and confused. ❤️