Because Yechan is always there to drag him out of his fears and darkness - adorable, lovable, caring, and sweet. Yechan gave him back his music and will be there to keep him sane while he tries to deal with all the emotions that come with playing again.
Is he drunk? But he was driving.. i just don't get it why he suddenly kiss yechan while all this time he has been trying to avoid yechan's skinship..