An actual evil mc??? Like evil evil??? Not evil for the sake of goodness??? Daym.
Well... yes. There is smut in the novel so the manga adaption should also have it. And as for the ending... it is a happy ending just not the happily ever after since...
SPOILERS
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The MC did pass away at 55 due to the curse but he also kinda reincarnated back a long time after and just pick up the ML who reincarnated as a puppy and flew away with the dragon causing the kingdom to be buried in a pile of snow. If that is what you call a happy ending then yeah. Also, the novel has the tag "dark" and that what I just described is not all of the ending so please read it first to understand what I meant
┑( ̄Д  ̄)┍
Yoojin be like, "IT'S YOUR TURN, BITCH!
(ノಠ益ಠ)ノ"