Michi and Niina didn't do it, because she unknowingly cried and they stopped. Her co-worker, the girl who had crush on Niina realized about Michi and Niina relationship, but didn't rattle her about it and just accepted she lost to Michi easily.
Michi thought she must put an end to this chaotic relationship. Much time later she told Niina they shouldn't meet anymore, which he complies. Although Niina now seemed to have his mind only thinking about Michi instead of his wife, Kaede. Kaede later sensed that something was wrong and decided to do her duty as wife and asked Niina to go out eat at the restaurant he proposed her (iirc), when they got back Kaede told him that he could do it with her but then Niina thought of Michi and apologized to Kaede that he couldn't do it now, she told him it was alright.
On youichi, michi's husband, side, it seemed that his and Michi relationship got better, but no. He was still pressured and his thing couldn't stand even after several times they tried. At one point, he finally snapped and told Michi about the pressure that's been weighing him down. Michi realized now that how much pressure that he had. As she cried alone, Niina saw her and tried to comfort her but after some talk they agreed that they should remain as co-worker from now on.
Youichi then had a talk with Mijima, the girl he had an affair before, and sorting things out, and they also finally could put their feelings for the better. Youichi for his guilt, while Mijima for her feeling towards him (she didn't tell him tho). Anyway, Michi tried to talk to Youichi after that and apologized for pressuring him, and everhthing seemed fine. They went to a restaurant later on and really, I thought this would be the end. But no. Michi resolved herself to change because she felt that while the others tried to move forward only she stayed the same. So she tried to dress better, and even joim an after work party with her company. This, however, put a suspicion grew in Youichi. He thought that maybe she met a man outside. Even though Michi just purely wanted to change herself for the better.
Meanwhile Niina and Kaede, when he said he had something to talk with her, she just said that he must've cheated on her. Which he couldn't deny. But she also said that it must be because of her, and as a man, he needed to relieve his pent up stress one or two times. Hearing that, Niina said that he never had that kind of relationship with Michi (he didn't said her name though). Though he denied of doing that kind of thing, it still didn't remove the fact that he was cheating. Dunno how they continhed this talk, but later on at work, Kaede couldn't let her mind off this. She thought that it was her own fault. And if Niina was just having a physical relationship with another woman, she could forgive her, but it seemed that she noticed that Niina had a feeling towards this other woman.
Back to Youichi, he asked Mijima to go eat with him. They talked, I wasn't focused what they were talking but in the end, when they were going back, Mijima suddenly hugged him from behind and confessed that she likes him. And that's the end of chapter 45.
Notes that this spoiler is not 100% exact as I just read a japan summary of each chapter but it's really just this frustrating. They should go to counseling.