Do you believe I'm living in mortal sin because I'm cohabiting with my significant other without being married?

I believe that my beliefs are mine, and for me, and only applicable to me. I believe that you get to do you as long as you aren't harming others.

Does this one act create a permanent and unbridgeable gap between me and God?

no... and a "christian" who thinks the above, needs to revisit christianity. (I'm over simplifying - but seriously)

If your daughter was living with a man in a committed relationship, engaged, would you remove her from your will? Would you refuse to support her in school?

oof... this is loaded... and heavy. first things first - I don't plan to pay for any of my kids' college - so there's that...

but to the rest of it... on the one hand, I can speak from experience: when your child chooses something you don't agree with, it's hard, it's complicated, it hurts, and it's just hard. But also, I actively try to choose the high road, to love more than to judge - to support more than to tear down.

Because if you dont believe those things, there isnt much to say. That's what they believe.

I'm sorry man. I know it's hard for you... it's also hard for them. They're lashing out because their illusion of control and hopes for things for their daughter are vanishing or already gone. I really hope they can widen their view to understand you're both happy together... and that is a good thing.