Fantasizing about my girlfriends sister and her boyfriend

I’m straight, but i think a little bi-curious. Ive been with my girlfriend for 3 years, and while she’s very hot, I always check out her younger sister, Erica, when we would go on vacation to the beach,etc. She fills out a bikini so nice, it always gets my blood pumping. Last summer Erica brought her new boyfriend, Mark, and my God. i always knew she was the kind of girl that could find a fit, good looking man, but fuck…hes so sexy. perfect abs, and looks like he could have a nice package in his pants. He def has a nice ass.. i can’t stop fantasizing about him and have to admit, I’ve masturbated and cummed thinking about him a few times. Usually I taste my cum after and imagine I just sucked his cock

Source: reddit.com/r/Erotica/comments/g9k5hx/fantasizing_about_my_girlfriends_sister_and_her