You have to figure - these things happen in "monogamous" or "one-to-one" relationships. You have SIX people. It can be overwhelming getting used to relating to ONE person in a new relationship and/or live-in situation (even roommates who are not sleeping together go through an adjustment period). You have SIX people. I'm surprised Thunder is the only one you're having an issue with (I say it that way because I'm not convinced yet that it's Thunder's "issue" per se).
Anyway, I'll say once more - you have SIX people, so you have, like, THIRTY-SIX different relationships going on (or something like that, give or take). I have to say that I'm impressed by the way ALL of you, INCLUDING Thunder, are handling this thing.