Filing status single vs Married Filing Seperate

I am married but have been separated from my wife for years. We've not had a divorce. I made the error of beginning this tax return with 'single' filing status and TurboTax returned an error. I spoke with my wife and she said she filed Married Filed Separate. When I went in the change this in my return, my taxes  owed increased by almost 15%. I clearly know very little about taxes and I don't know why this would happen. It's frustrating to say the least. She has already filed or I might try to convince her to File Jointly (seems like that would be the $ saver) but it's too late for that. Is there anything else I can do?