Our advice columnists have heard it all over the years—so we’re diving into the Dear Prudence archives to share classic letters with our readers.Submit your own questions to Prudie here. Dear Prudence, I’m dating a wonderful guy who I really care about. He’s divorced with a son and is a dedicated father—that is one of the many things I appreciate about him. His son is his first priority, and I completely understand. The problem is I find myself playing third fiddle to his ex as well. He swears he would never want to get back together with her. He seems...