He must've created it pretty early. I'm thinking he used his father's death for that Horcrux (love those btw).
And Merope? I don't think she loved V, just his father. And once he had left her she really didn't care about the child that much anymore. I distinctly remember the hoping he looks like his father bit. Obsessed...
Oh and hated how V thought that it must have been on the fahers side.