Personally, if YOU are LO's main caregiver and FOB doesn't help support LO or see LO, or is just an all around POS, then no. I wouldn't talk to him about it at all.
I am seeing a new man now, and he met LO for the first time before he and I even started dating. We were friends first, and that's okay. Meeting your LO is different than spending alot of time together. If LO will be spending time with your new SO/BF then maybe I'd consider it.
Unfortunately for FOB, I don't give a rats ass if he has anything to say about it! He doesn't help support LO, can't be bothered to come see him, BUT he can keep his older son every single week on his days off AND pay his ex wife child support!!!! UUGGHH!!!
That's just my opinion though... I'm off my soapbox.