Because you are not married, you will be considered two separate households for the purposes of determining eligibility for premium tax credits and Medicaid. If neither of you are claiming any dependents on your tax returns, you will each be considered as a household of one and your own income will be used to determine eligibility for premium tax credits and Medicaid as well as the amount of any premium tax credit and cost-sharing reduction you may qualify for.
If you are eligible for premium tax credits, you will each receive a separate determination of the amount of your credit and whether you are eligible for a cost-sharing reduction. Whether you can use your credits to buy a family policy rather than two individual policies will depend on the offerings in your state Marketplace. (26 C.F.R. § 1.36B-2(b); IRS, Questions and Answers on the Premium Tax Credit.)