Of course he is wanting Me Time alone at the gym, with his new body he is building ... the one he left behind in his lost youth.
Of course he is acting unusual, back and forth. He has one foot sticking through Alice's Looking Glass into the world of MLC. The other foot is in your world.
The C is not telling him a lot of stuff we are not telling you, for less. Work on yourself. It is about giving them time and space to get adjusted to not being who he was, ever again. His old skin no longer fits. He is not ready to wear his next skin, his older adult skin.
The C is listening to him process his issues and concerns. The C must accept his comments for the most part, to avoid driving him away. But the C will try to interject the voice of reason in manageable amounts. Give it time and feel good that he is getting help.
Keep updating and reading about MLC. It will give you strength. You will have to provide the patience.