Looking For Yaoi Manga

I read it within the past year. It's about a teacher who gets assigned to this school with supernatural students. There's one student who bites or kisses the teacher and that 'marks' him. The student disappears because he's turning into this demonic creature.

It's similar to this manga:
http://www.mangago.me/read-manga/sensei_kowai_hanashi_shimasenka/

I am trying to find a manga I forgot to book mark and I want to reread it. It is about this guy picks up a stray guy he found. Later in the story, the MC starts to put on a collar when he gets home. please someone help!!

I got the cd drama somewhere, but I haven't read the manga. I've been searching on google, tumblr, and stuff but still can't found the raw or eng translated. I don't speak any other foreign language other than lil bit of english, and a tiny bit of japanese (lol). So, anybody knows where can I found them?
And, oh, the other name is Cupid ni rakurai, or Kuupido ni rakurai.

I’ve been looking for this manga but I can’t remember the title ㅠ__ㅠ It’s an Omegaverse Yaoi where the omega got pregnant by the alpha but he didn’t tell him that he was pregnant cuz the alpha left to go work abroad. So after several years later, the omega was a full-time single parent worker. He was about to pick up his son, when he coincidentally met the alpha, the father of his child. Please please please help me! If you know the title of that manga, I would greatly appreciate your help!