Didn't Imogen say more then once that she really wouldn't have anything to do with him if they were out of the house, in a normal situation?
Now with her and Mikey getting all cosy, it shows even more how desperate people are to stay in the house. And Imogen is one desperate housemate.
Lets face it, she hasn't got much to offer other then her good looks.
So it would seem, Sezer is a free man, doing what he likes.