Thanks for the chapter!
I bet Angelos has a crush on MC. Would explain why so serious and strict with him. Also, he seems to have a knack for attracting elf females since both Dianne and Selenium are really fond of him. Also, what are the other females of the unit doing along with their rank and stuff? If Dianne was the only female in unit then the men's bath would just be the company's bath since she uses it at the same time as the men (likely to flirt with MC.) Therefore, there should be a women's bath for the other women in the company.
Selenium is really the MC's former girlfriend's uncle's cousin's aunt's daughter's stepson's god uncle's niece's former roommate! Seriously though, like Angelos said there are inconsistencies with her story but I think she really is head over heels with MC. My bet is she's the friend of the half elf who met the MC all those years ago that needed all that special spring water to heal a serious injury of some kind. The injury would prevent her from meeting MC back then but would hear all about him from the half elf who got the water. That would explain how she knew all those details, fell for him, was willing to wait ten years with her friend for him, and have her friend's collar. Not sure why pretended to be friend though although likely to have a stronger connection with him as opposed to being strangers who never met but heard all about him from friend, same with damaging her ear. Since she doesn't seem grief stricken the friend is likely still alive and in a stable condition without fear of immediate death but likely tied down to one place for some reason. Could be jailed, injured/crippled/sick, cursed or fulfilling a contract or bargain. Will have to wait to hear what happened to friend though, along with whatever MC decides to do if she needs help of some sort. In any case, think Selenium genuinely likes him but isn't being truthful about everything.