Which is the truth?

[MrCAS]

I would say something like:

I've been thinking about what you sent yesterday. I'm sorry that you feel my only intention to make things work is for D's sake, rather than out of love for you. It was out of my commitment to our marriage that I asked ex to stop communicating with me, even though this was a purely platonic and very limited relationship.

I wouldn't explain anything about the ex. The more you deny it the more it gives it life.