Does anyone else get this feeling out of nowhere and it suddenly shifts the way you look at your SO?
You stop trusting them and you overthink every little thing. They tell you everything is okay but you know it's not, even though they haven't done anything. You just know something's about to go wrong, you sense it, you anticipate it. It feels like they're becoming distanced and they don't enjoy talking to you as much as they used to. 
You can't figure out whether it's your gut instinct or paranoia. Your gut instinct never lies, right? Yet if you go with the gut instinct you end up ruining the relationship. If you go with paranoia you let yourself get used and manipulated, brainwashing yourself into thinking you're "just overreacting".
You try talking to them about their behavior but they tell you it's YOUR behavior that's problematic, not theirs.
They're talking to someone who you think is crushing on them. How do you react? You don't want to be controlling but you can sense something is off. Will it pass? Will it get worse? Are they already doing things behind your back? 
What's real and what's not? Which thoughts do you trust? Do you get the urge to break up, delete all your social media and distance yourself from everyone? Move away and start a new life? Stop dating forever? Yet you long for human affection as if it's something you can't live without? 

This is a common pattern I see in all my relationships. To top it off I have a bad habit of always falling for people as screwed up as me. Anyone else?