There were no commitments when you slept together, it was essentially an ONS. The fact that you've stayed in touch doesn't really change anything. It's nigh-on impossible to compete with an ex who they still hold a torch for, even if you're the greatest guy.. I think you're best off staying away and not getting attached. Give it a while for her to get over her ex and then you can maybe establish something from fresh rather than jumping in while she's still preoccupied with him.