Well...this is pretty much a train wreck in the making for Michi's and potentially Niina's marriage if she continues this route.
She finds Michi, she continues stalking her.
She finds out that Michi and Niina are getting together.
She confronts Michi, which leads to Michi finding out about You's infidelity, which leads to You finding out about Michi's infidelity, which leads to him finding about Niina, which in turn leads to his wife finding out...