We have provided this information in this Affidavit for the sole purpose of determining our eligibility for Domestic Partnership benefits. 2. Call your girlfriend's HR department or your insurance company and ask them right away.The affidavit requires essential information, including both partners' full names, addresses, birthdates, and the relationship's start date. A domestic partner affidavit can open doors to a wealth of benefits. From health insurance to family leave, it's an essential tool for many couples. The registration process is simple. There is usually an application to fill out which you can get from your city or county clerk's office. How to fill out the Affidavit for Domestic Partnership Benefits? The parties must be at least 18 years of age. We are eighteen years of age or older and unmarried; and.