why does my relationships only last about a month?

hello .. so, I’m 20 years old. none of my relationships really last. its getting to the point where I’m not sure if its because i have a problem and should see a therapist or maybe i just need some other opinions other than friends and my mother.

Longest relationship was when i was 17 which lasted a couple months after a year. after that i just keep talking, dating, getting into relationships that don’t last at all. closest i came to lasting with someone was a 6 month relationship.

last two boyfriends I’ve had lasted just a little over a month.
and now I’m with my childhood first love which we dated back when we were in middle school and it’ll be 2 months on the 24th and I’m completely uninterested. we moved Very fast (which tends to happen to me a lot)... i thought i loved him to death. he’s a good guy, clingy as hell, but great.
he kisses me, i don’t feel anything.. now I’m at the point where i just want to end it. but i don’t bc of Hope of course. theres some reasons as to why i might of grown uninterested but i don’t think they’re major to the point where one day to the next i lose complete feelings for someone “i love”
I’ve cried so many times thinking its my fault on why these things happen.

not to mention, i’ve been cyber bullied / harassed for 10 months and grew very depressed in the beginning, i feel fine now but maybe that has to do with it?

i do have to admit, i do get annoyed pretty easily. my best friend says maybe its bc i was raised an only child so after a while maybe i have low tolerance for others and thats why my relationships don’t last?

there can be so many possibilities. I’m sorry if I’m rambling. i just need some opinions. some help. I’ve never really been alone as well, i find myself always either talking or dating someone. i cling easily… looking forward to some answers..