We didn't sign anything, but I paid into his mortgage and he wants to reimburse me for my equity now that we're breaking up, but we have a lot of questions about how to do that.

I'm not even sure which flair to use for this, but perhaps somebody can help me here.

5 years ago, my partner and I got a house together, but only his name is on the mortgage. He paid the down payment and slightly more on the monthly payments, but we kept track of everything, with the express and mutual understanding that I would "own" whatever share of the mortgage I paid into, less interest, taxes, closing fees, repairs, with appreciation, etc.

We are parting amicably now, and the house has significantly increased in value, and he wants to reimburse me my share, but we have a few concerns/questions:

1). He's concerned that perhaps he should have been claiming the "rent" I paid all this time as income so that it could be taxed. This doesn't seem right to me, since it wasn't a payment to him, but towards the mortgage. If he's reimbursing me, it couldn't have been income, right?

2). The amount he's going to reimburse me looks to be about $25,000. We both agree on this amount, and he wants to give it to me all at once, but we want to avoid paying taxes as much as possible while still keeping everything above-board. From what I understand, you can gift an individual $15,000 per year tax-free, which leaves another $10,000 that he has to get to me somehow. He doesn't want to wait another year to do that, so how do we go about that? Since we never signed anything saying that part of the house was mine, we aren't sure how to classify/claim that money, tax-wise. Or even how to transfer it, honestly. I haven't looked into it, but I think banks have transfer limits?

3). He wants to create some sort of legal document that will prove that he paid me the amount we agree he owes me, but we're not sure who to go to for this. Any suggestions?

4). He wants to verify that the amount we have agreed on is correct. Would appreciate any formulas or algorithms that calculate home ownership percentages of multiple people over time taking into account down payments, taxes, closing costs, appreciation, etc. We created a spreadsheet, but don't know if we forgot anything.

We are in Washington, if it matters. Any advice, guidance, or referrals to professionals would be greatly appreciated.