my wife left and is prenant by another guy. i feel like i shouldnt have to pay for the divorce, how would i make her pay for the divorce?

my wife left me in january of 2012, she left and moved in with another guy she had been seeing behind my back for months but not sure of the date when it started. she came back in march but still was seeing him telling me she wasnt when i had my suspicions but no proof. she left again in may to live back with the guy she has been cheating with. now she is pregnant and she says its my baby and she wants to take me to court for child support and threatening me about it. she is approximately four weeks pregnant. we havent had any intercourse since around june 16th. she has been telling me she has been alone but two days ago she told me she has been living with him this whole time. the date she got pregnant, it wasnt by me. i feel like i shouldnt have to pay for the divorce since she is the one commiting adultry, how would i go about making her pay for the divorce?