First of all BTMODAD and mentsch1, seriously kol hakavod for sharing and chipping away at the stigma that exists way too much in the frum world which can really leave those who suffer in danger.
I also remember davening that Hashem end my life and partly envied those who were killed al kidush Hashem in E”Y back when I was there in yeshiva. B”H things are a lot better now, but as you can probably relate, life is constantly up and down.
Regarding davening that one should die I remember seeing a related teshuva in Teshuvos Vhanhagos (I think chelek 2 siman 82 amud 738), you can draw your own conclusions. But BTMODAD I like your attitude now and will probably be davening a similar tefillah. Hashem should accept all of Klal yisrael’s tefillos letovah!
As far as the original premise that Hashem only brings a nisayon that a person can handle, I heard that Ramban in Shaar Hagemul disagrees or limits this to specific situations. sorry I don’t have the exact mekor but would be interested if someone knows of this and can explain it.