My opinion is no.
There's an underlying current flowing somewhere.
Could be even his health.
I do recall in my twenties having periods of less but not what you are saying.
You've been with him like you said, his comment on his stressed out feelings, does it seem he's stressed more than he was when things were better.
Myself I would talk to him anyway and let him know you are genuinely about it and is there anything you can do do to help him,
For me stress was always released by sex. Maybe thats part of why I'm stressed more now, no hoochie coochie happening in my life. but some people react with stress differently. You could ask him what he thinks he could do to help release the stress.