My dad also has difficulty with speaking and sometimes with swallowing. The only advice I can give you is try to love and treat him as you did before the diagnosis. I think what has been really hard for my dad is that when he was told he might have ALS, all the family and many people in our town acted like he was already dead. We were getting sympathy cards in the mail, and every corner I would turn, people would be telling me how sorry they were to hear about my dad. I would tell him that he is doing good and is a fighter, and just asked everyone to continue to pray for him. I try to talk to my dad like I did before his speach became so horrible. Sometimes it is hard to understand what he is saying, but we manage to get the main idea of what he is trying to say. We make lots of jokes and try to keep his spirits up. He goes through phases where he seems down in the dumps though. It is tough to see your father to go through this, I know first hand. Also know that it is o.k. for your dad to go through many emotions. Some might be anger, others depression, or happiness. I think it comes with the territory.
Dana