It happened to me twice. First, there was one friend of mine who told me to let go when me and my then-boyfriend broke up. Few days later, I found out they were dating. **** that.
Nope, because whatever your friend went through with the guy/girl you'll have to go through to and if you didn't like what you heard about them then you won't like them in a relationship.
It depends how badly my friend's relationship ended since I wouldn't want to end up hurt as well. I would also talk about it with my friend. And make sure it isn't a one-night stand type of thing because I hate that and want a real relationship.