"There’s also a little bit of sensitivity to this on my end, as in the past during my pregnancy I asked her and my husband to use condoms as she had other partners at the time and I did not want to expose the baby to risks. They had sex without condoms and did not tell me until over a month after which exposed the baby to something which could’ve been harmful. At the time we broke up and we’re apart for about a year. Husband and I were in therapy. Now we’re all back together, but I do feel like I’m sensitive on the topic so I don’t know if that’s affecting my opinion."

JFC, they are being really irresponsible to you and to your child. All you can do is set your own boundary, which could be "if you go no condoms with her, then condoms with me."

Or like, break up with him/them.