<human>: First off I have horrible difficulty making friends and maintaining relationships and my best friend is currently basically my only friend. We do everything together. Also me and my sister have a very good sibling relationship. So the fact that either of them would ever lie to me like this is mind blowing. Also i'm not a very forgiving person.

My sister was having problems with internet connection on her laptop and during my attempt to fix it I noticed her recycle bin was filled with everything she's ever deleted in the last 2-3 years because she apparently doesn't know how to empty it. Well before I emptied it I noticed screenshot pictures of her phone with her and my best friend facetiming. I thought that was odd so I went through more deleted pictures to find screenshots of text conversations between the two and there's no question that they had been having a secret relationship behind my back.

It hurts me to know that they lied and disrespected me to have a secret relationship. The pictures were from a year ago but I don't know how long it went for or if it still is going on. I have not told anyone I know and I don't really know what to do. I've simply ignored all texts from both of them all day. What should I do?

Give me the gist of the text in a nutshell
<bot>: My sister and best friend had a secret relationship and I found out. How do I tell them I know and what do I do?