I have never understood why, but this apparently happens a lot.
I hope your BF gets better
I have sleep apnea. I think it has contributed to burnout a lot. Having a constant brain fog while trying to manage work and family is not good in the long term. I tried CPAP. It got the air in the brain, but disturbed my deep sleep, so I became normally tired during the day. I have a dental device which pushes my lower faw forward when sleeping. That seems to work with obstructive sleep apnea. I have made other positive changes in my life so I can't say for sure if it is just that, but my life has gotten better after I started using it. I don't know the term in english but Somnofit is one product I googled. Grown men need some nudging and even pushing sometimes and I am glad my DW did bring that up repeatedly.The apnea story is not going so well. My guy really struggled with using the apnea machine and has now send it back. I was really sad about it for a while. I hope he reaches out for help and guidance (from the general practitioner for example, or from the apnea patient organisation), but so far he hasn't. And he is a grown man with a functioning brain, so he can make his own decisions in this regard.
I don't have apnea and I don't know your personalities too well, but this is definitely the case for meGrown men need some nudging and even pushing sometimes