Spoilers below*
1. Throughout the series its hinted that Akatsuki (blonde-haired yariman*ref ch.3) has some sort of intimate relationship with Sensei. He goes to her office frequently and even has her cellphone number. However, in ch.62 he appears in her house casually going through her fridge. Its then revealed that she is his Older Sister (or perhaps sister in law) as that's what he calls her before he leaves. He hasn't made an appearance since.
-Ch.44, a girl who has a crush on Akatsuki thinks he is getting it on with Sensei, turns out he has asthma or some type of medical condition and thats why he see's her so often. MC then gets alone time with Sensei afterwards.
2. In ch.74, the Sensei has a wedding ring on. The MC asks about it and she states it's to prevent men from pursuing her, as she's getting ready to leave for a teachers conference. She only wears it this one chapter, but the ring did have an engraving on the inside of it. It wasn't clear on what it said, but at most it might imply that she had been married in the past or received it from someone long ago.(not sure since its left ambiguous).
3. In the same chapter (74), the MC and Sensei are walking together from his job, when some wannabe thug interrupts them. The thug recognizes Sensei and explains how in highschool he forced himself onto her and got her pregnant or something. MC is freaking out, but Sensei calmy tells the real story, in that the thug was just a loser virgin who wouldn't know where to put in in and ejaculated when Sensei moved her thighs. Thug gets embarrased and leaves, which confirms the validity of Sensei's explanation. She then tells the MC privately that she never did it with the thug and that his incident forced her to wear leggings/different clothes to prevent stuff like that happening again.
- Ch.50, Sensei has to go to some education meeting or something and is escorted by the PE teacher (gorrilla guy). Nothing happens and she meets with MC again to tell him she noticed he was watching her. She knows PE teacher is after her, but tells MC she can take care of herself and knows to be careful around him.(mentioned in a previous ch).
However, the story is not finished and things can changed or be added. I'm not a translator and there may be some minor details I'm missing, but that's is the gist of it. So far the MC and Sensei have been getting far more intimate in some of the chapters which I won't spoil. But from the looks of it, there's still no clear indication on where there relationship will end up. Hope this helps.