Boundaries in a second marriage?

We both have children, all about the same age. The difference is in the way we handle our exes. My ex and I deal with all things regarding our children cordially but keep our words to things kid related only. My spouse and his ex have this relationship that is still contentious, and my husband cannot seem to not get pulled into it, and it makes things uncomfortable. His ex openly disparages me to her children, and to those of you who are wondering: I did not break up the marriage, insist that the kids call me “mom,” try to get in the middle of the kids time with their dad, or disparage their mom ever. So, his ex just constantly berates him, and rather than just communicate solely about the kids, he’ll go out of his way to be ingratiating. When he does this it only makes her more hostile, and frankly it hurts me that he goes out of his way to be overly kind to a person who does nothing but spew venom about the two of us. I have asked him if he feels guilty about something because as far as I know the marriage broke up due to incompatibility openly acknowledged by both. His response is you get “more bees with honey.” I just don’t get it? His kindness makes her anything but friendly. Thoughts? Advice? Please, thank you!