I'm Not The Father of Her Son!

Thanks for your good work ma, please post this for me. Sometimes in 2013 my girlfriend got pregnant and said I'm the one responsible, later she moved in with me without any formal marriage rites done on her head, not that I don't want to but because i'm not too buoyant to finance both the marriage and pregnancy at the same time, though her mum was aware of everything. 
Later she gave birth to a baby boy who doesn't look like me in anywhere at all, it was then that I started having doubts about the paternity of the child. 
I called her attention on it and she still insisted I was the one responsible. Even when my mum visited to see the baby, she said the same thing while leaving. 
It was then that I made up my mind to go check for the paternity of the child but I hide it from her mum, I got the result today and it showed that I was not the real father. 
Please ma what will I do as i'm boiling and confused right now. 
The baby is one year and two months now.

Please do not break a bottle in your anger and do something that you may regret later in life. 
Now that you have known the truth, prepare for the day of celebration of the times you have shared with your girlfriend and her baby. 
Let her know that you desire to visit her parents for the formalising of your relationship between you and her. 
As she's preparing, help her pack all her things and let her know that you have decided that she wouldn't be living with you until you have done the needful. 
Also invite your parents and some relatives, the fewer people the better but their purpose is to be a witness to the truth you will reveal to everyone. 
At the meeting, appreciate everyone for their support and encouragement during your trying times and appreciate your girlfriend for being a good girl and understanding when she was with you. 
Then bring out your test results, make sure that you share the photocopies amongst each and everyone that is present in the meeting. 
Then let them know the genesis of your sorrows and pains and summarise it by telling them what you have decided to do. 
The reason why I suggest that you approach it this way is so that it doesn't look like you threw their daughter away without courtesy and respect for her family and her relatives. 
There's no sentiments or pity here so don't get yourself worried about what they might say or so. 
All you owe them is a sincere explanations as to why you wouldn't continue marital rites with her and everybody will have no option but to respect your decision. 
The good thing is that you allowed time to reveal the true identity of your partner and the father of her child. 
And I hope that you will take your time this time to pray before getting yourself entangled with a two timer.