Is it bad to date a friends ex?
If your friend still has feelings for their ex and had told you so, thats a red flag that dating this person is a bad idea. It can be tough to move on from a relationship when those feelings still exist, and it could cause tension if you make a move before your friend has moved on.
Should I date someone my friend dated?
I think its fine to date someone your friend used to date. So long as their relationship has reached its natural conclusion without your interference - for example, they didnt cheat with you - youre doing nothing wrong. That said, I recommend you talk to your friend about it.
Is it OK to date someone who dated your friend?
If it was a long relationship that recently ended, its best to let the dust settle. However, even if the relationship wasnt necessarily long in hindsight, your friend may still feel some sort of connection to their ex that may make it hard for them to be 100 percent OK with you dating them.