jealous guy

I was shocked to come across this:

“One night we were at a party and John went mad when someone told him his friend Stuart and I were dancing together. As soon as I saw the look on John’s face we stopped and, as so often before, I reassured him that it was him I loved. He seemed to accept it. But the next day at college, he followed me to the girls’ loos in the basement. When I came out he was waiting, with a dark look on his face. Before I could speak he raised his arm and hit me across the face, knocking my head into the pipes that ran down the wall behind me. Without a word he walked away, leaving me dazed, shaky and with a very sore head.”
--Cynthia Lennon, Good Weekend, October 1 (Fairfax; no link).

It's so hard to accept that it’s true, that John would ever do anything like that, even if he was a jealous guy. I always imagined him as kind and loving. Was I wrong about him?