The abuser won't show his/her true colours right away. They want to reel someone in - often being absolutely charming, doing a load of love bombing etc. They'll make you feel like a million dollars, they'll treat you like a queen. You end up thinking that you've finally found the Perfect Man. And it is perfect....until it's not. He'll probably mention tough times he's had with exes, and how badly they treated him. You feel sympathy towards this wonderful guy. You won't be the person to cause him so much strife. Everyone loves and respects him. You're reeled in, hook, line and sinker.
A few months in (it was about 6 months for me) and they then start with the small stuff. Small shit that makes you question whether it actually was bad or not. Oh and the odd bit of explosive behaviour...that swings back to gaslighting and blaming the victim. You end up giving the Abuser the benefit of the doubt. Abuser switches back to Perfect Guy (or Lady). You wonder if you're imagining things. They may try to isolate you from friends or family, stop you from doing your hobbies or studies or things that you love doing. They won't outright say it, but they'll chip at it...and you want to do all you can for this perfect guy and he seems so reasonable in his thoughts and requests. The shit escalates. The gaslighting starts. The reeling back continues. Before the victim know it, they're like a frog in pan of boiling water. They're a shell of themselves and they're utterly beaten down.
Why do they do it? Probably some fucked up power trip. They're out to destroy a person. To the whole world, they'll be a perfect wonderful guy, salt of the earth etc. They end up turning into their victim's worse nightmare.
I can say that my ex (from many years ago) didn't beat me up physically. He raised a fist to me, and he would punch the wall next to my face...but his MO was psychological and emotional abuse/coercive control. I was with him three years. I should have left at that 6 months point. He destroyed me, he wrecked my friendships, I stopped a uni course because of him (picked it back up afterwards, but had completely lost my confidence), halted my career progression at the time. By the time I'd left, I was overweight (emotional eating), and I had developed a stammer. There will be no convictions on my ex's record. I didn't go to the police at the time, and neither did his ex from before me (FWIW, I know we're both still labelled as "crazy exes"). Had this happened now, he'd possibly get done for coercive control.
In your position, I'd leave. But that's down to you. Stay safe, and I wish you all the very best of luck x