in death of a salesman why does biffs mental state deteriorate whenever biff comes home?

Biff blames his father for all of his own faults. In some ways, this isn't too far off the mark, and I think going home and being the "perfect" son who didn't apply himself brings out the worst in him...... he deteriorates. On the other hand, going home might just remind him of what he could have been, and the fact that parents may try to guide you down the path, but ultimately they're not in control of which path is taken.