The beauty of cohabiting is that in the event things don't work, one of you can walk out of the arrangement with little fuss, less damage and it involves just the two of you, mostly. But when a 'come-we-stay' arrangement results in a child, things can be a tad complicated.
As a man, you have to be a total jerk and heartless to walk out. Many in fact stay even if they don't like the woman, damn the consequences. But you can still walk, because there is nothing that is binding.