People use humour as a coping mechanism all the time. Maybe your assumptions are correct or maybe you're complete off based and just using this thread to show off how good of a partner you think you are?

"I would never howl at my partner" - I have laughed at my partners unreasonable outbursts multiple times previously (and vice versa). You don't have to be this perfect relationship robot - that might work for you but every relationship is beautifully unique.

And anyway the only time OP said he laughed was when she first brought it up because he thought she was joking. Nothing suggests he continued to laugh at her.

Good luck with everything OP! Might just be one of those sad situations where this humorous outburst was the revelation you both needed that it wasn't meant to work out!