Because they're going to see you holding hands with their ex, and remember how nice that felt, and if you think they won't envision you having sex together, you're being naive. His grades have dropped and he just got suspended from school for the first time for fighting. My ex-husband that I have been supporting both emotionally and financially while he was going through a rough few years I supported him because we have a child just informed me that he and my friend have decided to start dating. Not Helpful 2 Helpful 4.
Or it might be somewhere in-between.