<human>: Hi Reddit,

Just wanted a quick objective perspective. Basically my best friend, we'll call her Janet hangs out a lot with this girl we can call Betty. I only know Betty through Janet and my personality just doesn't mesh well with Betty. I witnessed Betty cheating on her boyfriend at a party and since then I've been avoiding her. I'm not on that close of terms to confront her about it. I am involved in a long-term, committed relationship so it hurts me when I see people cheating on their significant other. I was once friends with a girl who cheated on her boyfriend and I was just so uncomfortable I slowly distanced myself away from her. The annoying part is whenever I try to make plans with just Janet or post something funny to her Facebook, Betty either invites herself in or makes uncomfortable comments on the post. How should I go about "breaking up" with a friend? What should I say to my friend Janet who loves hanging out with Betty and sees no fault with what she did?

Can you summarize the given text in a few sentences?
<bot>: Introduced to a girl through best friend, she thinks that I like her a lot, trying to find a way to break it off with the girl and letting the best friend know about it gently.