This was the first picture Lavender ever got of Sage with Nick aside from the ones his mom took when they were all together. He only acted like a dad when she was around because of how much she had wanted grandchildren.
The first picture of her daughter and husband doing something fun together just because and it wasn't even really him. Her heart clenched but she forced that feeling aside. Sage was happy. She didn't know the difference. And she never would.
She was too little to remember Nick's indifference and resentment. She would only remember him being the way his replacement was.
Not Nick was a pretty decent dad. With the benefit of hindsight, Lavender realized that he probably only sat around watching TV because it was what she expected him to do. He did stop whenever Sage wanted to do something with him. He seemed to like kids.