I don't understand. Did ido actually pimp him out to his brother in the past life?

No. What ido intended was call his brother home and hand over evidences of that jerks crimes. But he came earlier. Sejin was in heat at that time and he thought that the gift ido mentioned was his own spouse in heat.
Honestly this story is just full of misunderstanding, lack of communication and as a result....angst (︶︿︶)＝凸