I got married in Mar 2019 My wife has medical Bills from Jan and Feb 2019. Can I use my HSA to pay her medical bills?
You can use your HSA to pay your wife's medical bills, since you are married at the time that you pay the bills.
IRS Publication 969, page 8, says:
"Qualified medical expenses [for an HSA] are those expenses that generally would qualify for the medical and dental expenses deduction. These are explained in Pub. 502, Medical and Dental Expenses."
Pub. 502, page 3, says:
"You can include medical expenses you paid for your spouse. To include these expenses, you must have been married either at the time your spouse received the medical services or at the time you paid the medical expenses."