what to do about a wishy washy babydaddy?

my ex and I split up recently and of course I find out I'm pregnant after πŸ˜’ so he's dating a new girl, and he's letting her keep him away from his 3 year old son.. apparently he keeps going back and forth wanting to be in his life, then not wanting to.. I don't want him to be able to pick and choose when to be in my child's life, but I also dont know how much is too much to put up with??? he hasnt seen his 3yo in THREE weeks.. and he'll say he's going to keep him for a couple days, then never does..Β