I think my one cousin was married and they had been trying for a little while so they went to the doctor to see what the problem was. It turned out the problem was her, so he dropped her like a hot potato (he then found a new girl, got married, and started having kids). In the other case, I think they were just going out and the girl's doctor had told her, for whatever reason, that she couldn't have kids. When my cousin found out, he didn't break up with her right away, but told her he would never marry her and they broke up not long after.
I've never heard of men doing it, but I have heard of women bailing when they find out the guy can't have kids. Some people just HAVE to have their own. I don't get it. I wonder if subconsciously they feel they are with someone who is defective.