Run.

Fast.

Just flee.

Emily, it shouldn't matter whether you have a partner or not or what complex feelings might be involved. As soon as children are part of the equation you need to get out.

If this man's number one priority in his life isn't his own kids then you need to question everything you think you know about him. Whilst he is gone you cut him out of your life. It might hurt but its the right thing to do and doing the right thing is never easy.

Block him on socials. Delete him from your phone. If you carpool or share a bus you find another way to commute. You future self and his kids' future selves will thank you for taking the hard path when he wouldn't.