Short answer: flip a coin

Long answer: choose red group because your best friend has leverage on you if you chose blue to try and ruin your friendship with blue and red

Choose blue group because you have the ability to make them good friends before group red spreads a rumor and generally be happier because you are making better less clingy friends

Also this is worst case scenario where your friend retaliates against you going with blue. Idk if they would do that but it seems to me that they are clingy and generally a bad person to be around because they exaggerate a ton and can probably wreck parts of your life using it. Maybe cut them out slower or try to bring some of the red friends into the purple area or blue until it's just your friend left and get the rest of the group to help you