Chloe has a BF?!
1. It'll make you look like a dickhead
2. It's not respectful
3. I don't see how a relationship could even happen.
Stay friends with her for sure, you never know what may happen, but do not, DO NOT try to convince her to leave him. That's a low blow and she will more than likely see that.
As of right now I say Lauren. It could work out? And if it doesn't, **** it.