Spoilers ahead for Episode 18 of Arrow Season 6, called "Fundamentals."
John Diggle has been an essential part of Arrow from the beginning, and he brought invaluable skills to Team Arrow as Oliver's right-hand man. Unfortunately for Oliver, he and his former best bro had a falling out that resulted in a brawl in the Arrow bunker and Digg making the huge decision to leave Team Arrow. Now, in seasons past, rifts in Team Arrow didn't always last for more than a handful of episodes, but David Ramsey (who plays Diggle) already revealed to CinemaBlend that won't be the case this time around. He also explained how Digg's decision to leave the team will continue to impact Oliver and the show moving forward, saying this:
Diggle and Oliver are still going to be able to work together in the fight to take down Ricardo Diaz, but according to David Ramsey, they won't be working together the way they once did. Digg will have a different kind of autonomy as an agent of A.R.G.U.S. (which just so happens to be run by his wife) than he did as Oliver's right-hand man, and given the events of the last few episodes of Season 6, it's safe to say that he and Oliver are going to have different ideas about how to do what needs to be done. The good news is that they seemed to be done with physically fighting each other after their blowout in the bunker. Hopefully that means any further disagreements will be worked out without battling it out on top of Felicity's computers.
Of course, Diggle won't be the only one in a new position moving forward in Season 6. In "Fundamentals," Oliver came to the conclusion (after spending the episode overwhelmed by Vertigo) that he needs to get back to the basics of vigilantism, and for him, that means all the way back to the basics. He intends to fight the good fight alone now, and he may end up needing Diggle sooner rather than later. After all, Oliver didn't really make all that much headway in his mission to save Star(ling) City back in Season 1 until he brought Diggle and then Felicity on board, and he may discover sooner rather than later that he needs to accept help. Perhaps learning to work with Diggle rather than expecting Diggle to follow his directions will set him on the right path. David Ramsey also told me this about what the separation will mean for Diggle in particular:
As much as Oliver has sustained loss after loss over the years on Arrow, Diggle has lost a great deal as well, and he hasn't gotten the chance to process everything in recent years. His time away from Oliver could help him grow and truly grasp how he wants to do what he wants to do moving forward. He'll have more to do than cover Oliver's back and give Oliver advice, and that may be for the best for both men. They might never have changed if they stayed partners and best bros because they wouldn't have had the necessary motivation for growth; as heartbreaking as that big fight and the subsequent separation is, both Diggle and Oliver may be better off in the long run.
We'll have to wait and see what happens next for Oliver and Diggle as they continue to deal with the aftermath of their big fight and split. Tune in to Arrow on Thursdays at 9 p.m. ET on The CW to see David Ramsey in action as John Diggle. Ramsey will also appear in an upcoming episode of another Arrow-verse series. Don't forget to take a look at our breakdown of superhero TV dates, and check out our midseason TV premiere guide and summer TV schedule for what you can watch on the small screen now and in the not-too-distant future.