Let's say that they dated just before his mom got sick, because I figure Michaela actually liked Les and their personalities probably get along alright. So once she started ~smelling~ Death she had to end it before it got bad because Michaela can't handle emotions, much less someone she actually cares about.

She probs kept her distance from him after that, especially if he separated himself from everyone. Now he's getting his shit together she's going to be super confused by him like wtf why would you want to be Responsible and an Adult?????? She's probably more willing to talk to him now though since he has way less death surrounding him and he's pulling himself together. I'm gonna say Michaela who normally is drawn to people who have death in their life, withdrew from Les because she cares about him. But she ain't gonna show that B(

EDIT bc ALSO Les realizing his role as gamekeeper or starting to step into that role, it'd be interesting if he found something about Grim Reapers and some connection to the Méndez' and brought that to Michaela's attention. BECAUSE SHE GOTTA FIND OUT SOMEHOW.