My boyfriends sisters cousin was my sisters boyfriend

Imagine this: you are a teenage 15 1/2 year old girl that has a loving boyfriend and a terrible sister that all she does is torment you and tease you. So she takes you out to eat but you guys crash into a tree. You get angry and argue, then you just end up turning the other way and begin to walk home. Then a stranger that's the same age as you asks you if you want a ride. You say yes, you guys fall in love, everything changes.