>>34130477After GSC, there was the Mt. Silver Training chapter where it shows that Red leaves on a journey with Green to train.
Yellow in FRLG states that she hasn't seen him in a long time. So either he met up with her to talk it out or she hasn't seen him in two years since then.
But Yellow is a lot more comfortable talking with Red when she does catch up with him at the Airship, so I think the former holds true that Red and Yellow are a lot more comfortable with each other.
But it's hard to tell with Kusaka's ass writing and the situation they were in was kinda dire and stressful with the whole Rocket Airship gonna crash thing.
For Misty, literally nothing happened.
For Blue, FRLG is the arc that actually tries to give more backstory for Blue which basically stated that Red was the one who helped her change into the person she is now and why she named her Jigglypuff after keeping it nickname-less for so long. Then there's the beach scene and Red's response with "I want to go with you," but nothing really happens out of it. It's kind of a dropped plot point.
TL;DR -
Red is on better terms with Yellow, Yellow isn't shy talking to Red at all in FRLG/Emerald.
Red and Misty probably didn't happen.
Red and Blue is a dropped plot point unless ORAS finalized volumes somehow wants to push for it.
Red is probably gay at this point. 
