What do you expect a girl to do when she's 18, has two kids, and no skills? "Shouldn't have gotten pregnant" isn't really a solution here. Let's say the guy tries to do the right thing and marries her. Lets say his salary is enough to support them, so she can stay home and take care of the kids.
You can't say "well, she should have..." that's not the issue and that fixes nothing. The fact is that she's 35 now, has 2 kids to support, and the guy has built his career with her at home. He now wants to leave for whatever reason. She deserves financial support. Now, if she's smart, she goes and she builds her own career or gets an education, but the initial problem is that you can't throw someone who supported you when you were a peon to the side and expect her to be able to support herself and two kids. It doesn't work that way, and for that reason, he needs to pay.
ETA: If that's gold-digging, then so be it. I don't believe so, because the girl didn't go seeking out a rich guy for the money. That is not my description of a gold-digger, but I'm ok with it, if that's what it is. lol