My Brother's Mother-in-Law

I'd been overseas for 10 years and the oldest of 5 (2brothers, 2sisters) I was still single, doing very well career wise. I returned for family events for short period and then left again. Finally, I returned to live closer to my parents and was 39 almost 40 on my return. My youngest brother 26 was also marrying his now wife, at the wedding I met her mother 42 divorced. A few days after the wedding I met her again and we started an affair; she wasn't interested in a relationship just casual no strings sex. But she got pregnant, still didn't want marriage or even a formal arrangement. Still visits me and sleeps with me now, our daughter has turned one last months. Only our family knows who her father is, they have accepted it without saying anything against our personal arrangement.