You know, I've been in a situation where I've been bruised, by my ex and by my late DH. The reactions to it were a different as night and day.
Ex "accidentally" grabbed me and bruised my arm when we were arguing. His reaction was that it was my fault, I wound him up, I should have seen he was angry and known not to push him by answering back. I didn't leave and it was the start of 2 years of escalating violence.
Late DH and I argued, I went to hit him with the TV remote (early in our relationship, I thought at that time that it was normal to react like that). He put up his arm to defend himself and block me hitting him, the remote slipped out of my hand and onto my face, giving me a black eye. He didn't touch me himself and was so upset, insisted on getting an ice pack, took full responsibility for not deescalating our argument, and then when things had calmed down, discussed his absolute red line of no violence in a relationship, and we agreed to move forward. He never raised a hand to me in 20 years, and I learned to trust and not to resort to violence.
Your partner sounds like my ex. I wouldn't say leave lightly (if the situation was truly an accident and he was apologetic, like my DH), but this is a huge red flag to me.