So he opened his eyes when he kissed him. This was the reason he was so mad?

i’m sure the (attempted?) kiss triggered him too, but we don’t get to know that yet. he did had a trauma back when he was a kid.

I personally won’t like it if suddenly my best friend (who I thought was straight) tried to kiss me when I was asleep xD so if taehwan was angry I can understand it (||but he has some trauma that made him like that||)

Yes, a person he trusted and felt he could let his guard down around chose to kiss him while he was asleep. That's a legit reason to be upset imo even without trauma making him extra sensitive about such things