Upside - it is a good question - what would be different this time. A wise friend of mine told me that when they are done with MLC we will know. Their actions towards us will truly change.
If you thnk it is another 'touch and go' you are right to be cautious. We invest a lot of ourselves when we give these people another chance, because we do it wholeheartedly. To then find they were just testing the water is incredibly hurtful.
This last round, with my xh apparently being so friendly, I was super cautious, because I was suspicious, and rightly.
I do not think you need to do anything. Take your time in replying to anything he sends you, and watch and listen. As Snodderly says, the answers drop into our lap if we are stay quiet.