What case can I file against the pregnant mistress of my husband?

I was married to my husband last 2007. We didn't stay longer after the marriage. I was pregnant with our child when we separated. He lived together with another woman and they had their son in the year 2009, a baby boy. We continued our own different lives. Until the year 2012, I processed some papers to buy a house and I need the documents of my husband and his signature for legally we are still married. That time..I don't know for what reason but we ended up making a decision of fixing our relationship. I gave him a chance to prove and fix everything. Sabi niya bigyan ko lg siya ng panahon na iayos ang lahat. I'm an OFW. Pagkatapos ng pag uusap naming iyon (June 2012) tuloy tuloy na ang communication namin. Bumalik kami ng anak ko sa abroad to continue my work at siya naman ay naiwan sa Pilipinas. I knew he was still living with his woman and son when I returned abroad. But he said slowly by slowly he is fixing everything para daw maayos at mabuo ang family namin ulit. In my next vacation June 2013, umuwi kami ng Pilipinas. At this time we went home to his place. We lived together again. After a month of vacation, my child and I went back abroad leaving him alone again. But he promised me not to see his mistress again. He will only spend time with her son without seeing his mistress anymore. I gave him my trust. Our communication continued. Until after 3 months I've found out that he was not only seeing his son but sleeping again in the house of his mistress every weekend. He said because of the child but he was not doing anything against us as husband and wife. I know it's so impossible that nothing happen between him and her the every weekend that he is staying there. But I still gave him my trust. This coming June 2014 I will go home for good already. I already resigned from my company here for he wants us to be together also. And just last week, my friends received a message from anonymous stating that the mistress of my husband is pregnant right now. I asked my husband about this. He kept on denying. He said he's not the father. The mistress also posted pictures on fb that she's pregnant. I don't know what to do. If ever my husband is the father of this child his mistress bearing right now, what case can I file to the woman?..thank you