My husband was an alien resident until 2006 then he left the country and lost his legal status, I kept filing my taxes as married filling jointly until 2015 then I switched to head of household did I do something illegal?

My husband was an alien resident until 2006 then he left the country and lost his legal status, I kept filing my taxes as married filling jointly until 2015=====> unless you get divorced from the spouse , you could choose to treat your nonresident spouse as a U.S. resident and file your return as mfj; If you and your nonresident alien spouse do not make the election to treat your nonresident alien spouse as a U.S. resident alien, then, you may be able to use head of household filing status. To use this status, you must pay more than half the cost of maintaining a household for certain dependents or relatives other than your nonresident alien spouse.
then I switched to head of household did I do something illegal?=====>>>>as mentioned above

thanks for the answer but it is not clear
my question was it legal by claiming my husband from 2006 -2015 take into consideration we are still married?
question #2 when I switched to head of household from 2016 until now was it legal?

my question was it legal by claiming my husband from 2006 -2015 take into consideration we are still married?=======>>as mentioned previously,yes. ince u are still married, u may file ur return as either mfj or mfs ... you


question #2 when I switched to head of household from 2016 until now was it legal?=======>>>yes aslongas you meet conditions with which u file ur return as hoh: you must meet certain criteriato file ur return as hoh. you must:Pay for more than half of the household expenses:Be considered unmarried for the tax year, and You must have a qualifying child or dependent