The Weatherfield couple will hit the rocks in the coming weeks as Sean begins to feel that Marcus is not spending enough time on their relationship.
Speaking on Daybreak this morning (June 13), Condou revealed that Sean's "self-centred" behaviour will begin to grate on Marcus - leading to a huge showdown between the pair.
Condou explained: "I think Marcus and Sean definitely love each other very much, but they are very different types of men. Marcus is quite a responsible, very caring type of person and he likes looking after Sean, I think.
"I think that's part of their relationship, and Sean's not really very grown-up and he gets jealous easily. He can be self-centred and a bit selfish at times, and I think ultimately that's going to be the thing that causes problems for them in the end."
The actor also appeared on Lorraine today and confirmed that Marcus's work colleague Aiden, who has a crush on him, will be back on screen later this month. Viewers recently saw a brief appearance for Aiden (Toby Sawyer) as an oblivious Marcus tried to set him up on a date with Maria Connor.
Condou said: "The lovely and very handsome Toby Sawyer is coming back. He's started filming already and he's back for a little while. So Marcus's love life is definitely going to get very complicated over the next few months!"
Coronation Street continues tonight (June 13) at 7.30pm on ITV1.