of doubts grow in your mind until it become a big tree that is hard to be removed.

Forget about the red flag, that will keep this incident always in your mind and you will try later on to reason things that your husband would do with/without his intention and associate it with this incident.

Maybe your husband put it in his pants to avoid a situation where he got embarrassed with what that lady did and see? He even forgot about it, I don't think that he would keep such a thing in his pants if his intentions were to really add her.

He is not looking for trouble indeed, to keep such a thing with him knowing that you would wash his clothes and find something like that.

Just try talking to him, play like you were surprised to find this there and what could it be. Don't start such a talk while you are upset with him or over something else, choose the right time and maybe you can ask for his help with your laundry and find a way from there to pull this note out.

Best Regards ...

Do not dwell in the past, do not dream of the future, concentrate the mind on the present moment. (Gautama Buddha)