Livre d'Or

Two thoughts.

The first is that you don't mention the pressures inherent in a job distant from your husband, and now quad. Well, you do sort of, by saying you would rather be in Cambridge, but you don't talk about the pressures that imposes on the job, and on your satisfaction with the job. If the dissatisfaction goes back several years, does that place the origin back when you got married/your relationship got serious? It may be the quad is just making something more apparent that's actually been true for a while.

WRT MK, no matter how good a friend he is, it's clear from what you say that he doesn't get poly relationships, and that is affecting his assessment of your plans. His thoughts may intersect with your worries, but he's discounting half the evidence (the value of your relationship to you) to get there. Give him time and his opinions may come around to value your relationships for what they mean to you, rather than discounting them to focus on the thing he sees as valuable, your career.

Actually make that three thoughts. I'm not saying this is happening, rather that it's a possibility that needs considering. Both the situation another friend is in, and my own experience with Evil Aerospace, make it clear that sometimes 'must improve' or similar assessments actually mean 'I don't like you' (my experience) or 'your face doesn't fit' (my friend's experience). Even if you think the assessment was valid, it's worth giving a little thought to your managers and whether any of them are a little 'off' in their interactions with you.