I have brought up two (Filipino) stepkids myself.

You need to have some serious words with your partner.

He should be the one to sort his son out and not allow you to be put through this.

It's just not fair on you.

Well that's my opinion anyway.

Oh, and the British family SHOULD work on the basis of people in a household respecting each other and not behaving in a selfish and intolerable way.
Naturally teenagers can be more 'troublesome', but you should not be suffering.