I think it's a bit unfair to say Alex has lost his sense of humour. He's obviously feeling a bit down at the moment because his best friend in the house is up for eviction. On top of that, he's upset because Jonny is making fun of something which Alex felt really strongly about. It may seem humourous to think that someone could make such a big deal about the 'weegate' thing, but it was to Alex, and it was Jonny's lack of understanding this that created all the tension between them. The fact that Jonny is complettely degrading his wishes again by, not only bringing it up, but laughing at it must make him feel uncomfortable.
He wasn't upset about Kate's impression - C4 simply cut off as he got into bed on a close-up to make everything look emtional.
At least Alex is trying to deal with the problem himself, rather than going off on one at Jonny. We may see him talking to Adele, or ranting about it in the diary room, but he's handling it in the correct way. He's making his feeling known to the one person he trusts in the house, and the diary room where true feelings are meant to be discussed. You can bet if the situations were reversed Jonny may have a thing or two to say!
I think Alex will improve after this week is over - whether Adele goes or not. I'm sure he'll be upset if Adele does go, but at least the waiting and the tension will be over, and he can get on with mixing with the rest of the group. This week has clearly been hard on him, for whatever reasons we see as silly or trivual. When he feels relaxed and liked in the house, he does have a good sense of humour. It's just, at the moment, you can't blame him for feeling a little left out from everything. If I felt alone in a house where everyone else appeared to be getting on really well, I think I'd feel a bit miserable as well.