Domestic Partner

So me and my Spouse have always filed separately I file head of house and claim my daughter as a dependent and he files single, we are not and have never been legally married. In order for me to claim him on my health insurance for a new job they require me to claim him as a Domestic Partner and I want to know: 1. Should I file the affidavit for domestic partnership and allow the insurance premiums to be calculated as imputed taxable income. 2. How can I expect this to affect me on my 2021 return, and 3. Is there a better recommendation for my situation.