> Does anybody have any advice on how to better myself and how to be kinder to him?

On this, you can take note of things he enjoys and spend some effort learning about them and/or doing them together…

However…

> Or even why I would be lashing out without knowing why?

You MUST figure this out as your number one priority. Nobody is going to be happy in a relationship with someone who abuses them, no matter what nice things they do when they’re not being abusive.