“so can I claim single or do I have to file as Married filing separate?”----> No. First of all, you can’t claim the Single filing status on your tax return as you are NOT considered unmarried on the last day of the year(if you are legally separated from your spouse under a divorce or separate maintenance decree, then you can file your return as single). As you are still married status, you can choose between filing a joint tax return or a separate tax return.As you can see, the married filing separately filing status provides fewer tax benefits than filing joint returns, but you will need to weigh the pros and cons and decide for yourself which is the best filing status for you; for example, if you choose MFS status, then you can’t claim Credit for the elderly and disabled , child and dependent care credit , or earned income credit or etc. Additionally, MFS taxpayers must both claim the standard deduction or must both itemize their deductions. In other words, you , as a MFS taxpayer, cannot claim the standard deduction if your husband filing his return as MFS is itemizing.
I guess another option for you(or for your husband) is to file your return as HOH; taxpayers claiming the Head of Household filing status benefit from a higher standard deduction and lower tax rates compared to the married filing separate. To file head of household, you must be considered unmarried( this means that you are married but lived apart from your spouse for at least the last six months of the year.) and have kept up a home for a qualifying person for over half the year, and paid more than half the cost of maintaining a home. As long as as of December 31 of the tax year, you had not lived with your husband at any time during the last six months of the tax year, and qualifying child ,i.e., his child, adopted child, or stepchild lived with you more than half the year. The child does not have to be your dependent if you have stated in writing that the noncustodial parent may claim the dependent exemption.