MC is an idiot, isn't he. He has such a crush on FMC that he doesn't realize that she's just a snake in the grass. He even pushed a cute girl away right before the sex with her because his first time should be with FMC? So he either thinks that FMC is still a virgin (what I highly doubt) or he doesn't care about her not being a virgin but still wants to stay pure for her?
The friend of MC seems to be a real bro at first impression, setting up MC with a cute girl that was into sex with him. But I smell some drama about his person, just a foreshadowing. I wouldn't be surprised if he starts to aim for FMC too, hitting on her successfully with the result of having sex with her before MC. Just to add some typical korean drama.