Our sex life has declined significantly over the years?

My boyfriend and I are both 30 and this year marks a decade together. For most of these years we have had a great sex life and I had no complaints. His libido seemed to match mine, he'd last forever (15-20 minutes) to the point that I'd be lifeless from so many orgasms, and we'd easily do it 5+ times over the weekend.

Now we are a bit older and I totally understand that things are different (work, stress, body, etc.), but I have been begging for things to "go back to the way they were" (not exactly, but closer to) but it's like I'm with a different person. 2-3 times a weekend if I'm lucky, but usually less, <5 minutes each time, nearly half of the time he loses his erection before we start (and if this happens, once he does get erect he doesn't last), and I've spoken to him countless times about our sex life trying to understand how someone wouldn't be aware of such a big change, even if it was gradual. Why would it only be me bringing it up?

He has told me that in the past he would "prepare" for me to come over by masturbating before the weekend. I questioned why he doesn't just do that then? And he mentioned being more busy with work (less free time to prepare). I suggested that we schedule it which he agreed to. Twice on Saturday, once or twice on Sunday. This isn't working..

This morning he lost his erection right before entering, and it's the second time in a row this has happened. I literally just got up and left, I was so embarrassed. My thoughts were racing wondering if it's because I wasn't perfectly shaven or maybe he's just no longer attracted to me. The first time I was getting on top and he lost it, so I'm thinking it's the view (looking at me? my face? my hair (messy from sleeping)?).

Just looking for advice, especially from those in long term relationships on whether things can ever improve, or if this is kinda it and I should expect them to keep declining. I so badly don't want to give up on us, but it's out of my control and I just want to stop feeling this way about myself.

Thank you.

TL;DR: My bf and I's sex life has declined over the years, and he struggles to perform a lot more. Talking doesn't seem to work and makes things worse, and I keep begging for things to go back to how they were before which I'm not sure is possible.