While I completely understand it's natural for posters to tell OP that this would be a red line for them, I don't think it's particularly helpful.
It's almost akin to victim blaming.
If OP decides to stay in the relationship (assuming this isn't repeated behaviour and there are no other red flags) any judgment from other people isn't helpful.
I should have name changed for what I'm about to say, but don't really know how so what the hell.
I was arrested for drink driving in my very early twenties (now in late fifties so thankfully way in my past). Not an excuse in any way, but I was fleeing a potentially dangerous situation and I was just over legal limits and kind of shopped myself.
Not that withstanding, I felt utter utter shame, embarrassment and horror about what I'd done and the consequences that followed.
Had my family and friends had a firm red line that's being expressed on here I just don't know what would have happened.
I didn't even apply to have my license back for seven years because of the shame I felt.
Needless to say it's not a situation I'd EVER put myself in that place again.
So to suggest that OP should blow apart their whole life is a huge assumption.
If their DP has form for this reckless behaviour, or if their relationship has shown a propensity towards selfish behaviour, then there's no reason to ditch their whole lives over this.
It's not helpful.
We should be supporting OP during what will be an horrific time in their life while they work out themselves what is or is not a 'simple' red line.
If we condemn someone for one act of reckless, dangerous stupidity, then we are saying that redemption is never possible.
I don't want to live like that.
Had that been the case in my situation then I dread to think where I'd be.
I wouldn't have gone on to have the life I have. I'm more than thankful that redlines weren't drawn for me.
N.B. Obviously this doesn't negate the fact he's committed an horrendous crime and should be punished accordingly.