Pregnancy and sex, need advice!

Currently 7 months pregnant with my first, me and my child father don’t talk at all. We was some what good in the beginning of the pregnancy then he completely changed. I haven’t seen him in months and he ignores my messages. Now I’ve finally moved

I started talking to a guy from my past (an old fuck buddy). I’m starting to lust over him again, all I think about is sex when talking to him. I want to but have doubts. He’s gave me reassurance and we talked about it in full details. Clearly I’m single so why do I feel like I’m disrespecting my child’s father if I do.

Any advice?