How to split home after a cash out refi with girlfriend

[Thomas Loyola]

Hi all, I'm looking for ideas on how to fairly split home ownership after a cash out refinance with my girlfriend. The thing is, she owns the house and doesnt qualify for a refinance without me. She has about $120k in equity and we are seeking about $25k. With both live together in her townhouse. She owns it 50/50 with her dad, who just wants his down payment back when we refinance. She's lived there for about 5 years and I just moved in with her about a year ago. We've been together for 3 years. We have similar incomes and split all bills and mortgage evenly. We are very happy and I can see myself popping the question in the next year or so, but we both want some sort of insurance in case things don't go as planned. Even though I'd be half responsible for the mortgage, I feel like expecting half of the equity would be unfair since i kind of just dated-into this equity. Any and all ideas are welcomed and appreciated! Thomas