Yeah, it makes sense that you would have to post less often. I'm sure it'll get easier as the little guy gets older, though kids will always need a good deal of time and attention at least until they're ready to go out into the world.
Whatever you decide to do about poly, it sounds like just talking about it with A has opened some interesting discussions and increased your emotional intimacy level. So there is one thing you can indirectly thank M for, she introduced a new level of communication into your lives.
Hope the stomach issues recede!
Love means never having to say, "Put down that meat cleaver!"