Ruka and Tai are mates. When an omega is in heat they can only do it with their perspective mates. Therefore, Tai only comes when his heat comes since their not lovers. They are both in love with each other but Ruka feels that he is a nuisance so that's why he acts indifferent towards Tai. As you can see from chapter 2, during the the wedding reception Tai's aunt started talking about Tai's mom condition and when is he going to have his own kids. This affected Ruka that's why to push Tai away Ruka asks Tai to come over knowing that Touma was coming over. Ruka's intention was to let Tai know that he is already seeing Touma. Since he stated that Tai feels responsible.
To summarize everything Ruka feels that Tai's feels a sense of responsibility towards him. That's why Ruka is always saying he is a nuisance towards Tai. Even though Tai is actually in love with Ruka. You can see from his expression at the end of chapter 2. He looked happy that Ruka invited him over since he would only text him when his comes. They both need to communicate. I'm bot sure yet why Tai bid him or how it happen. But I can only tell they are having big misunderstanding. Thats what I understood as I read it.
Sorry it was long and its all ocer the place, I have many thoughts and even I'm getting confused as I write.
If it's about what just happened in Chapter 2, basically Ruka is trying to end things with Taisei so he called up his friend to help him be his preetend "boyfriend" so it would look more convincing as to "why" Ruka wanted to end the relationship without Taisei finding out that Ruka actually likes him
Thanks for helping me understand
NOOOOOOOO!!! Σ(っ°Д °;)っ
I don't get it ??