How do you come over/over come the "what if" dielmma?

Good Evening/night/morning,

(note: ain't the best title, this is just what i can think of, it's midnight and just off work 2hrs ago, so forgive me for my grammer mistakes plz. i can't handle that. )

so, i thought about what's really affecting me mentally the most and it comes down to 2 things, hating myself and what if's.

and what if's just increases the hate. but at the same time, what if have given me some of the greatest idea and helped me of thinking of some just great fantasy stories.

(imagination)

i can't stop thinking of all the mistakes and stupid decisions i made when i was younger and every time i think of it, i always end up of thinking of
"what if i did that" and i get "oh, you would have been in......."
and the more the i think the more it just spirals

"don't you regret it now?" "what a f/// idiot you were" "can't eve do shit properly" etc...
and when it's a mistake i fell into multiple time, it just gets bad, like bad bad,
i come out, just wanting to forget about everything and just not existing.

"what a retard you are" "no wonder you can't reach (goal)" "no wonder you're failing in life" "just give up"

and what i do to handle all this is walking but it's tiring me man. It helps, especially during the cold. Just numbs you. i can't think of the cold and negative thoughts at once.
so i forgot and just focus on not freezing. but my legs are also tired and my body will give up on me soon.

gym, work, and walking back and forth to both places is tiring me out. I just want peace.

i finished writing my essay for last week about my childhood and man i just remember when i had nothing to worry about and didn't understand much.

i have thought about just ending myself and just give up but i can't. more like i don't want to give up for some reason.
i have a hope for something that i don't know.

and i can't stop thinking about all these what if.

only way is to busy myself but my body need a break but so does my mental space. so what do i do.