My reasoning is very much the same as yours, thinkkank. It is what it is and indeed inevitable, so basically the thought that the good times are over, and I'm just prolonging the bad, or at the very least meaningless times to face the same outcome. Sounds pretty stupid.
Of course some miracle might occur the day after I kill myself, but really it seems far fetched and no longer reasonable. Have waited long enough, run out of patience and I'm tired, don't care anymore, not least because now age and other issues are also grinding away at me. What's more, death doesn't frighten me for various reasons, and it's something every being on this planet went through at some point, which makes it almost trivial. Death is a gamble, maybe a door to something better, or at least different, and if there's nothing else so be it. The only reason I don't completely agree with @thrw_a_way1221221 and @theguineapigking is that I don't hate life, never will, and I'm going to kill myself because I loved it and can't live it to the fullest anymore. I'm sick of compromising only for it to get worse - I quit.