Love doesn't exist for me it sucks

relationship problems

Well I have always had relationship problems and those who know me know that
But I'm here seeking advice, information, and other stuff bcs I tried basically everything to make one relationship last longer than one week yea sericly can't have a relationship any longer than that and that's if they said yes I'm mostly rejected
But I try to have a great relationship but it never works out this how it goes I have a crush on someone and finally get the courage to tell them I like them and ask them out this is what happens I either get rejected admidatly or the say they don't have the same feelings or they will say aww but I'm taken tho but if I do manage to get one to say yes this is how it goes we are like how regular relationship start then a couple days later they either cheat on me dump me for no reason or just leave without saying goodbye
I just don't understand it like why would someone do that to me but this has happened since I was young so now when my crush says no I'm just not as fazed by it like I ust to be even tho I get upset about it and let down
But yea that's how my relationships go anyone have any suggestions that I haven't tried yet