Sounds as though you have way too much emotionally to deal with by yourself. Might it be possible to get some counseling for yourself?--and, hopefully, with someone who is able to get your dilemma and help you emotionally distance yourself more from it. Your parents' drama, and that of your father's fiancee, belongs to them, not you. And it would be helpful to be as kind and nurturing toward yourself right now as possible. The less you react to their acting-out behaviors, the better for your own welfare.

I've written about self-soothing and self-validation in earlier posts and you might want to google these two terms along with my last name and see whether you can get some additional ideas on what must be a really distressful situation.

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