Coleen says

I think honesty is the best policy here. If you feel weird talking to her face-to-face, then call her up and tell her. And just be honest about the situation – tell her it wasn’t planned, but you really like each other and you’ve been putting off breaking the news because you don’t want it to be an issue in your friendship. And ask her how she feels about it.

Initially, she might feel awkward too, but she might also be OK with it. She’s not with him any more, so you’re not doing anything underhand, and obviously they split for a reason. It might be a case of good riddance!

But I’d bite the bullet and sort it out sooner rather than later, as running around cloak and dagger style, hiding from various friends, can get pretty tiresome.