In Steven W. v. Matthew S. (1995) 33 Cal.App.4th 1108, the mother was legally married to Matthew but was cohabitating with Steven at the time the child was conceived and born. During her cohabitation with Steven, however, the mother stole away "on a romantic weekend tryst with Matthew" and became pregnant. ( Id. at p. 1112.) The mother, child and Steven lived together as a family for about two years until this triangle came to light, at which point Steven left the mother but retained shared custody of the child. Ultimately, both men asserted parental rights to the child, and blood tests revealed Matthew was the biological father. ( Id. at p. 1113.) The court found that Matthew was entitled to rebuttable presumptions of paternity based on his marriage to the mother when the child was born (Fam. Code, 7611, subd. (a)) and the blood test evidence (Fam. Code, 7555). Steven, on the other hand, had parented the child in all other respects and was also entitled to a presumption of paternity under Family Code section 7611, subdivision (d). Using the weighing provisions of section 7612, subdivision (b), the court held the presumption of Steven's paternity controlled. "The paternity presumptions are driven by state interest in preserving the integrity of the family and legitimate concern for the welfare of the child. . . . The courts have repeatedly held, in applying paternity presumptions, that the extant father-child relationship is to be preserved at the cost of biological ties." ( Steven W. v. Matthew S., supra, 33 Cal.App.4th at p. 1116.)