Imagining fp/partner with someone else

Does anyone else struggle with imagining scenarios where their partner is with someone else/planning to sneak around with someone even if you don't know who? My bf said he might get home late today and I immediately started imagining that it's because he's going to go to see someone else.

I feel so stupid with this type of thinking but I also get so sad and feel abandoned the minute I see a small glance or goddamn eyebrow twitch out of place, like just because he's on his phone it means he must be talking to someone else. His tone was a little off? He must hate my guts. I don't know why all the love he shows me goes out the window the moment I start feeling this way. I feel so, so crazy and self-pitying and I just want to know how to STOP thinking like this. It's draining and I know it puts a damper on the relationship and puts pressure on him because I sure as hell wouldn't put up with someone as needy and clingy as I am. So why do I act and think that way?? He left for work hours ago and I have things I need to do but I'm just stuck sitting here feeling sick and unwanted because of my own stupid made up thoughts.

TL;DR - Do you imagine your partner/fp with someone else and if so, how do you deal with those images/ thoughts and jealousy?