Can I stop my husband from getting a divorce?

My husband moved out of our house about a year ago and now says he is filing for divorce. We’ve tried to get back together a few times since he left and he’s stayed here at the house with me several times. I read online that we have to be separated for a year before he can get a divorce if I contest it. We’ve had sex as recently as two months ago. I want to contest the divorce because I still think we can work it out. What do I need to do if he serves me with divorce papers and how can I prove that we have not really been truly separated for the one year period?