Boyfriend hardly finishes in bed anymore....

I 23 Yr old female and 23yr old male have been together 3 years. At first he didn't really finish from sex the first few months because prior he watched too much porn/ masturbation. But after a a few months he did with no problem and pretty much did for the longest time everytime. Then one day he just hardly finishes from sex again and he doesn't even masturbate anymore.

For the last year especially the last 6 months he has been on a downward spiral of mental health having depression and alot of stress.

I hadn't mentioned to him often as didn't want to make him feel bad but in the last 6 months he has hardly finished at all. Occasionaly his had a problem staying hard which was never ever a problem. The sex is great and he says his satisfied but he does not finish. Occasionally I might say and ask about it which sometimes then makes him want to finish then he does. Other than these occasional times he just doesn't unless I mention it.

I just wonder how long this will go on is it simply the stress and depression possibly. Do I need to do more like tell him I want him to as that seems to work sometimes.
Anyone else experienced this kinda thing, what do.you think of it I'm.not.sure how to feel. Sometimes it gets me down as I feel like I'm not satisfying him.enough.