Again and again, the single mom's posting have said that they were in a "supportive relationship" or something similar before they got pregnant. Then, the guy cut and ran.

This is the one thing that has not been clearly stated and then rebutted. And that is that such relationships are ALWAYS that way. What do you expect the guy to tell the truth and say? "I really only want the sex".

The world is full of such guys and not surprisingly, many have relationships with more than one woman at a time. What they have in common is that they are physically appealing and have an ability to convince women that they are "the one". Therefore, women are afraid that if they don't do what it takes (agree to regular sex) to keep them around, they'll lose them. Unfortunately, too many women believe that it is critical to attract such a guy - for their self esteem and the adulation of their peers and often for the genes they will pass on to their children.

So, if he won't commit to you and then build a life together before having children, its very unlikely, he will be there when you have one without planning. But don't expect sympathy because you based your decision on this slim hope.