From the time they first hooked up at the end of S1, it was clear Lawrence saw her as a rebound. Which makes sense, when you go from leaving your longtimee SO you lived with and are fucking someone new that same day, that's not something designed to last.

But he can't be honest with himself and admit that's all Tasha was to him. So now he comes to her wanting to make it work, which isn't something he really wants. But now that she's going to be drawn into a long term thing with him, it's going to end poorly.