How do I claim my tax credit for health insurance if I am married and filing separate because we split up and she is now being claimed as someone else dependent?

If you are married and you file your tax return using the filing status married filing separately, you will not be eligible for the premium tax credit unless you are a victim of domestic abuse and spousal abandonment and can meet certain criteria. Details regarding this relief are in the instructions for Form 8962 and Publication 974.

Generally, a taxpayer who lives apart from his or her spouse for the last six months of the tax year is considered unmarried if the taxpayer files a separate return, maintains a household that is also the main home of the taxpayer's dependent child for more than half the year, and furnishes more than half the cost of the household during the tax year.