i just went through this and i can tell you, you will not stop looking for clues and second guessing everything for a long time, if ever. i got back with a girl last october. right away her sister showed be all the drug stuff they had been finding in her room. my gf swore up and down she was clean. within a month she said she maybe needed help. she hasn't gone for help and now five months later she has a warrant out on her and is still using. i've really cut my story short and can tell you the whole thing if you'd like. what i can tell you though is trust your gut. i knew something was wrong, but i ignored all the signs. the lieing, manipulation, and worry just got worse and worse until i lost myself. its only been about three weeks since i packed up stuff up, but i am starting to see things more clearly. unless your girl is making a serious effort to change her life, the addiction will tug at her until she caves.
i can tell you that i now question in my relationship was an entire lie. i question if i really knew my gf, and i know she doesnt know herself. it was difficult to leave, but it has allowed me to see that i can havea better life with a healthy person. i worked harder at fixing her life than she did.
this board helped me through difficult times, there are a lot of great experienced people here. you need to look out for you. good luck.