3 options 1. Sahn isn't so bad (not to Dojin) and he is just sad bcs Dojin never told him about this. So he is just in shock. And sad. No big deal. 2. He has been in love with Dojin. 3. Something with Taehwan... like Sahn is jealousy bcs he likes Taehwan (and if is that it means he had something with him in past). But the third option is not very likely.
3 options
1. Sahn isn't so bad (not to Dojin) and he is just sad bcs Dojin never told him about this. So he is just in shock. And sad. No big deal.
2. He has been in love with Dojin.
3. Something with Taehwan... like Sahn is jealousy bcs he likes Taehwan (and if is that it means he had something with him in past). But the third option is not very likely.