Is there a scene where Michael is confronted, notices actively or even
mentions something about their love?
In Dunder Mifflin Infinity (S4E03), Kelly asks Ryan:
Kelly: Can we speak privately about our relationship?
All the employees are in the conference room (including Michael).
In the episode Koi Pond (S6E8), Ryan says the following:
Ryan: Some of you may have noticed I'm in a kind of ill-defined
relationship type of thing.
Michael: Okay, what do you want me to write?
Ryan: Just put 'Kelly'.
We can safely assume that he is aware of it, and it's possible he realizes it's only a one sided relationship (Kelly really loves Ryan, but Ryan takes advantage of Kelly).
Why it's possible Michael knows it's a one sided relationship?
Michael can be aware of small details.
- In Halloween, he's aware that Pam sometimes allows calls go to voice mail.
- In Fun Run, he knows that Pam's computer crashed because she downloaded an adult video.
- In Koi Pond, he attempts to convince Jim to wear a certain watch, because the client knows style and they're trying to sell success.
- In Heavy Competition, he colour codes all his information so he knows not to say anything to the client.
- In Scott's Tots, he clearly remembers the names of all the students and their hobbies.
It's likely he has the good sense to stay out of it, knowing that it would likely end when Ryan decides it no longer benefits him.