When do you tell her?
This part is possibly the most painful but the most important.
Jo says that although there is no perfect time for this conversation, being open and honest with your friend is best done sooner rather than later.
"There can be nothing worse than discovering via someone else that you’re dating her ex, even if she appears to have no further emotional investment in him," she says.
"It won’t ever be a pleasant, easy conversation and you may get an angry, jealous or hurt response. Be brave, let her have her say and reassure her that your friendship will always be important."