Cumming on friend's sister's stuff

I go visit my friend around once a week, and when I went to use the bathroom, I noticed that his sister's retainers were sitting right there for me. I rubbed it all over my balls and dick at first, and that's when I realized I could cum in it so that she can walk around with my sperm in her mouth the entire week. Each time I visit, I make a deposit all over her retainer and toothbrush. I was thinking about storing all the cum I get throughout the week in a container, and then when I do go to their house, I can completely submerge it for a few minutes so that she can completely get all of my jizz in her mouth. Is it normal that this turns me on, knowing I have a girl with my cum always in her mouth?