Need help w/friend

Angelina basically nailed this one imo..
Has happend to me before, I was quite pissed because of it.. was a long relationship.
Thou it happened the next day after we had broken up so I knew what was going on...
Few other factors come to mind of why I was pissed off but thats not relevant here..
Angelina said it best, it depends soely on how close they are in the relationship.
Also for some, it whould depend on the 'best friends' intentions who are dating your ex.
Such as if their only using them for something, or if they are in it for a true relationship.