Responses
Because he felt cornered upon realizing that this killer knew about his private life, and the police didn't believe him when he tried to report it. The 2nd time he went there was in order to try and secure some evidence of that dead body to protect himself, basically. Once that failed, he just kept getting more and more entangled and trapped in the situation.
And I reckon we might get a bit more information on Seo Ilmo's thoughts in the next season, hopefully. (For now, giving away his thoughts would probably be too revealing and take away the suspense, in my opinion.)

Really curious as to what 2nd season could be about
A lot of this season was self-narration by the uke and very little on the seme's thoughts so its hard to swallow what's interesting here
Like okay, you found out he was a murderer but you keep going back to him? Did he have a reason to keep seeing the seme aside from money?