Suspicious
I recently remarried at 39 and I have an 18 year-old daughter whom I've raised. My wife is 42. My daughter is still in HS and lives with us. She liked my wife (her step mom) from the moment they met and they spend a lot of time together, unfortunately shopping and running up credit cards, but that's another story.
I've caught them a couple of times when they have come into the house and they give each other a hug and a kiss. The hugs are fine, but they kiss on the lips. Once I saw my daughter slip her step mom some tongue, but she stopped when I walked in on them. I might be crazy, but I think there is something going on between them. I don't know how to talk about this to them without coming off like a paranoid dad/husband.
Voice activated tape recording his somewhere and you will know in time.
Exactly what I was going to propose. Set up a camera and record it