If you are still legally married your filing choices are to file married filing separately or married filing jointly. Since you have no contact, filing a joint return seems unlikely since you would both have to agree to it. You do not say who you are paying child support to, but child support is not entered on a tax return. Child support that you paid is not deductible.
So....sounds like you file MFS. You will need to enter some information about your estranged spouse. (what have you been doing for the past eight years?)
If I am filing a separate return why do I have to list my spouse’s information on my return?
Even if you file separate returns (the worst way to file) you each have to list each other's SSN's and some other information on your own tax return. The IRS can then cross check to make sure you are not "double dipping" for itemized deductions, dependents, etc.
If you are in a community property state, there is more information that will be needed.
Community property states: AZ, CA, ID, LA, NV, NM, TX, WA, WI
https://ttlc.intuit.com/questions/1901162-married-filing-separately-in-community-property-states
https://turbotax.intuit.com/tax-tips/marriage/five-tax-tips-for-community-property-states/L4jG7cq7Z
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
