Stepmother finds her stepson masturbating in the pool and volunteers to help

I'm on my way to the pool to spend the hot day, but to my surprise, I see my stepson masturbating. I notice his big cock, so I surprise him, and he sheepishly tells me that he can't hold back because his girlfriend hasn't taken off her new outfit, so that makes me horny, and I tell him that I can help him with my pussy. He accepts, and we fuck hard in the pool without my husband suspecting anything.