I think Andy has made a serious and concerted effort, more than once to help Jason, and Jason is in a grump and won't be helped. He just needed to process a bit.
Andy found it a bit frustrating that he couldn't really help, and was also concerned - the convo with Alex was one of concern and excuse.
If a friend is really withdrawn and difficult you tell others that they are a bit upset to help protect them a bit and garner some tolerance and sympathy. That's no backstab.
Andy did enjoy himself at the party, they ALL did, even Jason some of the time, that's okay isn't it?
We don't know that he abandoned Jason, he could have asked him if he was okay and Jason just told him to go and enjoy himself as he'd get over himself - we don't know.
As for the diary room, it was a little off, but Andy's had a few and was silly and I don't think he meant any harm at all.
BB like to make MOUNTAINS out of small things, we've all seen it. It really doesn't signal some realignment or anything else. Just a bit of 'out of sync' stuff. And Jason was truly in a determined sort of grump. I think he'll be over it by tomorrow.