You two clearly have different come-froms on financial issues. You appear to be operating from mismatched assumptions.

First piece of advice for you is expect no payback for the 6 months you supported her. That was your decision, live by it.

You need to come together on this. You need to come together at a higher level than the details of what percentage of mortgage each of you pays.

I think you are overreacting to be considering divorce over this. Money is a difficult issue for many couples. You need to give it some conscious attention.

If you want to get dark and technical and look at it from the perspective of, "What would happen if we divorced?" She would be entitled to a piece of the house in divorce. Because of this and because she's benefiting from living in it, she should be contributing to the mortgage.