I had that thought.
But also the thought that maybe he isn't making up the difficulties that he has (with his mom wanting him home right after work), and that this means maybe he can't be the kind of friend he was before.
That doesn't make him a horrible person; it just means that's not how things are going to work out.
So stop asking him; stop pressuring him.
Also--if he's getting flak from the boss about how work attitude, etc., he may be feeling pretty stung, and so he's pulling back. He may also want to concentrate on actually accomplishing work, since that would be his big argument should he get further criticism. He may know that there's not too much he can do about his bipolar affecting his work attitude, and so he's just going to knuckle down and get WORK done, so that if his boss complains again, he can say, "at least I got X amount of work done."