I kind of understand what you're talking about here, Sanctus.
I've experienced myself, that when I had a good relationship with someone (could be friendship, could be acquaintance, or even with a co-worker I really like), that, upon meeting their friends or other people they can interact well with, and seeing them interact with them, it often makes me feel that suddenly I'm standing there liked chopped liver. Like, I find it more difficult to sustain the good rapport I share with that one particular person I'm fond of, when there's one, two, three or more others around them, being friendly with them. This is in great part because I find it more difficult to keep up social interaction with a group of people, as opposed to with someone one-on-one. And yes, it does lead to an instinctive feeling of "I don't like that the other person is suddenly taking up so much attention from my friend/acquaintance/cow-worker etc., I want that attention to go to ME, like my attention goes to THEM!"
Rationally, I know that that's childish, but I can't help feeling that way sometimes, and I keep it hidden in the recesses of my mind, so I don't let it interfere with anything.
But yeah, I can get jelly, a little.
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clarity of thought before rashness of action