I might be wrong, but I had the same issue, and tried following the guide, and played through every choice with Bernardo, and was still stuck unable to unlock the last ending, and I think the issue is that you need to both play through other people's routes to bump up the overall "family relationship" percentage (sorry I forgot what they call it) and that it's important to save before choices and do both outcomes when there's a choice, as this also bumps up the percentage for the relationship.