I didn't reply on your other thread, PP, not least because I had a feeling that it was more complicated than it first appeared, which is definitely how it seems now that you added more detail here. Before I thought, "Well, maybe your mum was just being kind about your current DP being a fellow human being, too".
Plus, she said she was wrong before in her assessment of how you used to feel about the ex-P, so why would she be right now in her assessment of how you feel about your current DP! Therefore, current DP shouldn't credit anything she says too much, should he?
But on basis of what you say now, it really sounds like your mum is how mine was -- one of these people who says too much her own opinion, even when it's only opinion, and (almost on principle) doesn't remember to keep quiet because of how it might affect other people's feelings and lives.
Why don't you "trust" your DP? Do you really mean that you don't want to open up with him, because of all this painful Sh*te?