I don't understand the ending between sya and lei. Can someone explain it to me please

Basically, when Lei died and Sya brought back his corpse an angel came and made a deal with Lei, he would bring him back to life in his body, but only if he managed to get Sya to choose him over the child "Lei" he was making, if Sya finished making his fake "Lei" then Sya's soul would be annihilated. In the end, Sya finishing his fake child "Lei" so the real Lei is now gone and can only watch Sya and the fake be happy now.

Honestly, nobody got a true happy ending. It's sad.

That's sad need to reread it since I already forgot it. Thanks for explaining