I agree, their relationship is incredibly tragic. Of course Wesker's more human side could have been chalked up to trying to manipulate Chris, but I feel that showing emotion (especially happiness) would be something rather alien to Wesker considering his upbringing. I think his small smiles and laughs would be genuine and, after discovering more about Wesker's past, Chris would realize that and it would hurt all the more knowing that Wesker had shown him something so beautifully vulnerable and human no matter how infrequent it was.