Yes I studied psychology too to certain level. But I never heard of parents' role to determine child sexual preference. If that was the case, the whole argument dies here, and that will be the proof that homosexuality is the result of nurture. There isn't anything like that.
But if you are talking about the parents' role in child's psychological development, then sure separated parents has some effects, but then again, that depends on the single parent role who will raise the child, if it will be enough or not. But we are talking about gay couples here, and not separated ones..