Hard and fast General Rules For Everybody make sense with some things and not with others. Some things are generalizable. Others are not. What makes very good sense for some folks and their unique situation may not make good sense for another.
If I'm having emotional challenges of any kind, its best for me to share about it with those I'm closest to. Not doing so is unhealthy for me. It hardly matters what the reason is for the challenge I'm having. It's just better for me not to attempt to bottle it up or keep it from someone I'm close to and hanging out with. I'm also not capable of hiding or concealing my feelings when I'm in emotional pain, so anyone close to me is apt to ask "Hey, are you alright?" and I'm going to be presented with a choice to tell the truth or make up some bullshit ... or perhaps say "I'd better not say." (etc.)
If I had another partner other than my sweetie, and my Sweetie and I just had a difficult moment together..., and then I'm with my Other Sweetie, well Other Sweetie would pick up on it. If I did talk with Other Sweetie about where it hurt and why, I'd probably do so in a mature and sensitive way so as to take into account everyone's feelings and needs. That's what maturity is all about: the ability to do that. Some folks aren't so good at being mature in this way, and perhaps they should just keep their stuff to themselves because of it.
A mature person tends not to engage in blaming others much for how they are feeling, so there's not much need for side-taking and all of that "triangulation" stuff (which rhymes, by the way, with strangulation). I can talk about my feelings without blaming anyone. But I'm old now and have had lots of practice.