Listen, Meghan, I'm 42, and I can tell you with absolute certainty that we are both of us in our best years now, with many more still to come. You couldn't pay me to go back to my 20s. Your fear that you wasted them is based very largely on how unhappy you've been during the last few years.
Even if the marriage can't be salvaged you didn't waste your time with it -- it was an extended lesson that was necessary to get you ready to make your next chapter (whatever it is) AMAZING. So don't beat yourself up for that, make use of it.
Ever hear of the song "God Bless the Broken Road That Led Me Straight To You"? That title is like a mantra for me.
This experience will only have been a waste if you choose to waste it. Go be strong today.
Me42, H40 D12, S8, S7 A revealed: 7/13 Sep 4/14; Agreed to D 1/15