SUBREDDIT: r/relationships
TITLE: Me[18M] and my girlfriend [19F] of 6 months broke up and I am very confused.
POST: Well, me and my girlfriend had been seemingly very happy together in our relationship.  Over the past month though, it seemed like she wanted to talk less and less with me.

Yesterday, my friend got on one of her friends nerves who took it out on my girlfriend who subsequently broke up with me.  She said that she needed some time to figure things out for herself, which is fair enough I understand that and I want her to be happy.

We live about an hour away so we both have our own groups of friends and only really hang out when we are dates and whatnot just the two of us rather than with others.  Her friend then told me that she apparently cheats on me "constantly" and then proceeded to say some of the nastiest things that I had ever heard about someone about her.

I personally had been advising her to cut contact with this guy as he had been a bad influence, with hard drugs and other things that you really do not want to get in to.  She kept vouching for him, but yesterday I guess finally decided they shouldn't be friends.

Really I am mainly confused about whether I should believe the friend who says that she cheated on me, or if I should believe her who says that she never did and may want to get back together once she figures herself out.
TL;DR: 
Odd breakup with girlfriend leads to confusing situation about her faithfulness towards me and whether or not I should consider getting back together with her.