very sad looking for advice

my ex and i broke up 3 weeks ago. we were together for 8 months literally everyday. i found out he lied about hooking up with a girl i know 4 months in (while he was hooking up with me.)

i couldn’t trust him after that and i was always getting mad at him for the smallest things. besides that reason, we both were sometimes bringing out the worst in each other.

i initiated the breakup and he made sure we stuck to it. he said i make him feel like he’s losing my mind cause i couldn’t handle him liking girls IG pictures.

i begged him to come back and of course he just wants to be on his own at this point.
logically, i know this wasn’t working but i feel so much regret.

i haven’t bothered him in over a week and i just really feel so alone and sad.
it’s really getting to me and my only friend lives across the country. my coworkers are tired of hearing about it. and my therapist is helpful but can only do so much.

advice on how to truly stop this overthinking loop? i keep blaming myself