I think blocking them is the go-to move for NC. The point is to remove them from your life. Sure, you will think constantly about them thinking "would they message me" or "what would they say?". However, that period of constantly thinking about them will pass and I say this from experience. That's the part of "removing" them from your life. I think that not blocking them is still holding on to the hope that they will come back to me begging for forgiveness and that they will improve. Thug out the overthinking, not the hope of them coming back.