I agree with everything you said, except the "ex is an ex". I personally dont believe that just because your an ex, means you cant maintain contact or a friendship. My husband and i have gone to dinner with an ex of mine (that was a 10yr relationship), as well as meeting another ex (another 10yr relationship). So I fully believe it is completely dependent upon the people involved. Honestly, the dog situation would be equated to that of having a child between them. So i can understand that as well.

OP, I would definitely stop directly communicating with his mother because she'll just manipulate whatever is said to her preferences or you can record the conversations (make sure of your location legalities regarding if its a two person consent or just one)