Maybe you guys can help me.
I've had my 2 boys since they were 9 weeks old. They are 3.5 years old now.
My Fletcher is afraid of EVERYTHING. This morning broke my heart though. Last night he was sitting on my lap and I found out I got a really good grade on a midterm exam. My boyfriend put out his hand to high five him, I did and Fletcher gets soooo anxious and nervous and afraid of the slapping noise. He leaves and won't come near us, he tucks his tail between his legs and slinks off to the kitchen to his bed and won't come out. I don't know why he is so afraid. This morning my boyfriend jokingly threw his arm up and Fletcher cowered in the corner of the bathroom and flinched big time and laid down, he looked TERRIFIED. This dog has NEVER been hit! NEVER! My Dexter is oblivious to it, he does not care about the slapping noises and all that, but Fletcher acts like he is a beaten animal. I hate it!

It makes me sad, but it also makes me wonder WHY he does this. He is not ever hit. He may be yelled at once in awhile when I catch him marking in the house but never hit. Boyfriend spoils him rotten and would never hit him either.
Any ideas? How can I build up his trust/confidence? How can I figure out why he acts this way?