Who was to blame

[sandgrown]

Last night DP and I went to a comedy night with friends . Friends picked us job. We had a lovely evening. When we got home we realised neither of us had a doorkey and teenage DS had gone out !
DP went into meltdown even though in my eyes we were both at fault for not checking we had keys. Apparently there is no way it was his fault because
A I was the last to step out of the house and should have checked. There was no need to lock the door as DS was home and I didn't need car keys.
B DS should have rung us and checked we had keys before he went out . Our phones were on silent throughout the show and DS would expect two responsible adults to have a key !
C It could not be DP' s fault as he had been so busy cooking dinner and washing up he never thought to check . DP had cooked dinner for the first time in six weeks and I had washed all but one dish that was soaking .
Lovely friends , who studiously ignored DP' s rant, drove us to pick up DS (only 5 minutes away) and the situation was resolved. Who was to blame?

*He will often tell people how his ex wife left him and moved away with his boys but omits the fact he had an affair ( not with me).

He sounds a peach.

To be fair I'd expect the last out th door to check to be honest.

Past that he sounds like a bit of an attention seeking drama llama.

He sounds like my ex, a real selfish 'world revolves around' me twat.

He isn't going to change and you said is now blaming you in general?

What are the positives?

Both to blame but no big deal and easily resolved. He sounds like an idiot.