I Have Been Jerking Off To My Girlfriends Sister

So as the title suggest, I've been doing exactly that. Up until she turned 18 she was just kind of a passing thought but after she turned 18 (she's 20 now) she has been wearing more revealing clothes and noticing more and more features on her. Like an amazing rack and amazing DSLs. I've been thinking about her and jerking off to her for over a year now. I'd love to feel those lips more than anything down around my waist.