I’m with chicken soup, actually. If the dad won’t marry the mom, she does truly have the responsibility alone, for all practical purposes. Marriage is legal security for both parties. ‘Planning to stay together’ is not. imho. My son is in the same situation, so I have also seen this close-up and personal. If his ‘wife’ left him bc he would not commit, some of the blame would be squarely on his shoulders.
The hidden assumption here is that he has the right to force her to marry him.
Suppose she doesn't want to get married?
How much cocaine has to be snorted to come to the conclusion that dad won’t marry mom?
Mom was playing the field.
Mom may want to party and a baby gets in the way.
One sex partner? She doesn’t want that.
If the baby is around being raised by dad she might feel guilty.
If the baby is adopted by people she will never see then that reminder goes away.