Am I gonna lose the case?

Yes- you can win the case if you can prove that the child is not yours. You must bring a special proceeding in family court in the county in which the child lives to demand a paternity test. As long as you have a good faith basis for believing the child may not be yours, the court will order that the mother have the child's DNA tested, and yours must be tested as well. If the test results show you are the father, whether or not the mother of your child had multiple boyfriends before during or after her pregnancy is irrelevant- the child is yours and you must support the child. If, however, the test proves you are not the father, you do not have to pay child support.