Will I Be Held Responsible For Child Support In This Complex Situation?

One year ago, my casual girlfriend of 4 months became pregnant, under much pressure from her and family, we married in soon after, against my better judgment. Baby was born. The next month, I discretely took an at home paternity test without her knowledge and sent it in. The test came back no match. My name is on the birth certificate as father of the baby. Our marriage is in poor working condition. If we were to seek a divorce would I be held liable to pay child support? Is there a limited time from knowledge of paternity until action is taken to not be held liable? I do not want to procrastinate if I may end up paying for someone else baby. Should i tell her that I found out that the baby is not mine?