YA romance-girl has to move in with sister after mom goes missing

-book about girl who had to move in with her sister because her mom is missing, she is found in her mom's trailer(I think?) and is forced to move because they can't find her mom
-high school-aged, can drive so junior/senior?
-sister has just got engaged/married and moved in to a really nice house (she is like 10ish years older so they were never close)
-sister's neighbor has a son who is the girls age, he used to swim(and was super good) but had to quit to help his dad and his dad's business
-neighbor has a pool
-wears the key to the trailer on her neck
-sister's house is close to the mall and sister sends her to go get clothes like the firstish day
-she hates the neighbor at first but they fall in love, until he does something really stupid but they end up together anyway
-everyone at school hates her
-I read this like 3 years ago and don't remember if I loved it but it's been bothering me for like a year so I have to read it again- THANK YOU

Sounds like Lock and Key bySarah Dessen