Sean's relationship will hit the rocks in the coming days as he becomes jealous and concerned over Marcus's friendship with work colleague Aiden. His paranoia soon leaves Marcus (Charlie Condou) furious, leading to a shock split for the couple.
However, Cotton today (June 20) told This Morning that he can understand why Sean gets so annoyed over the situation.
Cotton commented: "Sean, all of a sudden, is jealous. Well actually, there's a reason why, because Marcus has spent loads of time with Maria and now this Aiden's tipped up, so it's getting on his nerves, I think. That's quite understandable."
The actor said that Sean's fears may not be entirely unfounded, hinting that Marcus and Aiden could indeed become more than just friends in the long term.
He explained: "It's not the case at that moment. But we must all learn to honour our instincts, because I think that Sean's instincts might prove to be right. And I can't say any more than that!"
Cotton suggested that Marcus's desire to be a father is another reason why the relationship fails.
"They do want different things," he confirmed. "Sean already has his son Dylan and it's a big responsibility, so he doesn't want to do something just for the sake of keeping something going that maybe has run its course."
Coronation Street airs Sean and Marcus's troubles next week on ITV1.