SUBREDDIT: r/relationships
TITLE: How do I [f/20] end it with my boyfriend [m/21] of almost 5 years?
POST: I'm sorry its kind of long!
We've had some rough patches but these past few months have been ok. He recently told me he "loves me but is not IN love with me" but that we would try and work it out. 

Ever since that day he's been very distant. We rarely speak or see eachother now. I recently found out that he's been talking to another girl behind my back. They've been flirty but nothing too serious that I know of. 

 I didn't want to end it but I know I need to before I get my heart broken. My question is how do I do it if he's avoiding my calls. He's pretty much my best friend so do we still hang out after the fact?
TL;DR: 
boyfriend  is being flirty with another girl during a rough patch we're trying to work out. How do I break it off before my heart is broken?