It's not bad.I understand why, because you know eachother's pain.
I think you are both drawn to each other because of your mutual loss. You know him because he was your best friend, she knows him because he was her boyfriend
I understand that but please also understand when a person is grieving sometimes they start relationships they shouldn't. At least I did when I lost the love of my life. I needed a grieving period and I didn't take it.
I say it's cool, but there's always a risk of her comparing since uve always been close, or rebound reaction. Good luck.
you sure do, the odds aren't in ur favor unfortunately. Give her lots of space, and take it super slow.