Sadness to Happiness

My wife died in a car accident with her parents, and I (36) was left with my 2-year-old daughter. At the funeral was my sister-in-law (32) 5mths pregnant with her son at the time, the father of the child had left her pregnant and broke and so her had been living with her parents. But stayed home the day of the accident due morning sickness and not wanting to go shopping. I was living in our forever home as my wife called it and my sister-in-law (SIL) was staying the condo her parents had at a retirement village. Which had to be sold shortly after the funeral, so my SIL needed another place to live and moved in with me and my daughter. Nothing happened between us until after the birth of her son. No straight after a few months, it started slowly as we were mostly together and most, we met thought us married. Especially with a newborn and 2 years old, my SIL didn't try dating and then we just kissed one evening and slept together and as they say the dam broke. She slept with me every night and almost 4 years after she moved in, we married. We now have 3 children to raise my daughter, her son and our son.