My mom is a flight attendant and away 2 to 4 days a week leaving me at home with Mitch who my moms been with more than 3 years. I'm 19 and 2 years ago my mom and me moved into his house. I always got along with him well and feel comfortable around him. I did notice how he would look at me if I were out back by the pool wearing my bikini. A few times he saw me in my bra and panties and I know he saw me naked a couple times when we first moved in. Each time my mom went away he seemed to try and catch me undressed and seemed to know when I was taking a shower. I didn't notice for a few months but he would knock on the door asking me to give him something out of the bathroom. Sometimes a bandage, a towel or lotion. The side wall has a full mirror and it finally occurred to me that the door only had to be open a few inches and he could see me through the mirror. Funny thing is I wasn't mad about it and still have never said anything and he keeps doing it but always when my mom is away. With the weather here he mostly goes around in shorts with or without a t-shirt and I have to admit he is a cute guy. Sometimes he only wears his boxers even when my mom is home. When she goes away he started wearing these silky underwear that is sheer. A couple times a week he only has a bathrobe fully open and I see his penis and balls. He comes out from his shower naked with only a towel over his shoulder and many times I see him with an erection. I go back to school this month but its close by and I'm home every afternoon. About six months ago was the first time I ever saw him jerk off in his room. He leaves his door open a bit and knows what time I get home so I know he does it on purpose. I not only don't say anything to him or my mom about it but I admit I like watching him. Once or twice every time my moms away he knocks on the bathroom door. Shamefully I make sure I'm naked letting him see me through the mirror sometimes having a short conversation with him to prolong his seeing me. Its like we both enjoy exposing ourselves but we have never spoken of it and pretend its not happening. My mom would die if she knew about this or how excited I get by seeing him or him seeing me naked. When he jerks off he is usually naked in his bed and never looks towards the doorway but must know I am either in the hall or watching from my bedroom. It excites me enough that I masturbate never letting him see me. When my mom is home I almost always have underwear on but when she isn't I don't wear any in front of Mitch. I have even gone downstairs many times with only a towel wrapped around me and boldly expose my rear and vagina. its turned into almost a game we play on each other where we are both exposing ourselves to each other without mentioning it. I sometimes sunbathe topless knowing he is home but when I come in tell him I didn't know he was. Its amazing how we act so innocent in front of my mom and I'm sure she has no suspicions about anything.