My female best friend just broke off a long term relationship, and now she's acting bitchy/slutty.

Alright, so my best friend is turning into this person that I never knew. She is turning into an everyday girl that I see all the time and it's making me upset to see this happening to her. She is not acting like herself at all when she is with this one friend of hers who was a nice girl who is now a slut. My friend is a senior in high school and is starting to make friends that are my age (I'm 20, so a 2-3 year age differential). I care about her because we laugh and have such a great time together but lately in the past 3 months she has changed to the point of one time when she was with that one girl who I think is changing her because she completely ignored me when I just drove 2 hours to go hang with her dad to go surfing, and her mom tells her "you know he is standing right there" and she replies "Ohh hey" in a monotone voice. She admitted that she did this on purpose not to me but to my friend and so now I'm upset with her and I don't know whether to be pissed off at her or just be her true friend and just talk to her about how she is feeling. Any suggestions on what I should do to make this situation better? She means a lot to me and to lose her would suck but she's a totally different person because the way she texts me is not nice and her photos on Facebook and Instagram are getting more and more revealing.

This girl is a triathlete in high school with a 4.6 GPA, and a beautiful talented person and ever since this breakup with my best friend, she has been hanging out with the wrong friends and the wrong crowd. She has been drinking a lot (she was against drinking before) and partying every weekend. It is sad to see this and I don't know what to do. Any suggestions? I've known this girl for a while so please don't say get rid of her, unless that's the only option. I want to help her because I think the drinking and partying is just covering up the real problem which is her feelings.

She is also ignoring me as of now because she thinks I like her because I wanted to talk to her about this and she kept on asking what it was about and I dumbly put "You and I" and she said "i only like you as a friend, please don't make this friendship awkward". I wrote its not about a relationship, its about what happened at camp, and now she won't write back to me. I honestly do like her but my best friend just broke up with her and I'm not looking for a rebound because she is vulnerable right now. I want to become her best friend first before we even think of becoming more than just friends, and we are/were really close friends.

So my questions are:

1) Should I be mad at her or should I be comforting/ be there for her?

2) She brought up me liking her, and there have been times where I thought she has liked me but I don't know if I should bring it up, or if it's brought up should I deny it and say I want be her friend when I honestly do like her but telling her that right now would be the worst timing possible in my opinion. Lie to her or myself?
My female best friend just broke off a long term relationship, and now she's acting bitchy/slutty.
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