Yes, you love each other. Yes, there’s nothing you wouldn’t do for each other. That’s not the point. When money is involved, a formal agreement is how you show respect. A simple promissory note might be all you need (a quick web search will lead you to free forms). It should spell out the terms for repayments. Technically you can give any individual $15,000 a year without any tax issues (or $30,000 to a couple). But above those amounts you definitely want to charge interest to stay in the IRS’ good graces, and report the interest as taxable income.
The rate you choose should be no lower than the applicable federal rate (AFR) set monthly by the IRS. Some good news: It’s very low. In May, the AFR for loans with a term of less than three years was 0.25%. For loans running from three to nine years the AFR was 0.58%. The rate is fixed; your borrower keeps paying the initial agreed-upon AFR rate for the life of the loan.