Ex Daughter In-Law

When I retired from the military, I moved to where my son and his wife lived. I had divorced 6 years earlier, and he was the only child we had. He had a baby girl, and I became the main caregiver for my infant granddaughter. When she turned 4, my son and his wife, Casey, got a divorce. It was a mutual thing and it ended on good terms, so I continued to be the main person to tend to her. 4 days a week, I would travel to their respective homes and babysit while the parents worked. Casey is a beautiful young woman, 5'2", curvy, with nice tits and a big ass. She'd had never acted seductive or slutty in the years she was married to my son, but as time went forward, I began to notice changes when I'd come to her house to watch my granddaughter. About 3 months ago, I came into her house and sat in the den watching the news as she was getting ready. (This was the normal routine and the baby usually slept until after she left for work.). She came walking through the den with her hair still wet (not unusual) wearing jeans and a bra (no shirt). I was sort of taken back, but she seemed perfectly comfortable in standing in front of me wearing a lacey push up bra while chatting a bit. A couple of weeks later, she did the same thing , only this time her bra was lacey but see through. I could easily see her areolas and nipples. I realized this was intentional to get a reaction from me. This happened a couple of times, and then it became panties and bra. About a month ago, she was already in the kitchen when I arrived, came walking out completely naked, and said, "Don't mind me. I'm just running late this morning." Instead of covering up or acting embarrassed, she stopped to fumble in her purse for her eyeliner, all the while naked. I have to admit, I got a hard on looking at her. Now, I see her naked most days as she pretty gets dressed as the last thing she does. I play if off as no big deal, ans I'm certain she wants to fuck or at least get me to make a move. I can't do that as I t would ruin my relationship with my son, and if I do, she will stop letting me see my granddaughter.