To be perfectly honest, if you just want him to be happy, geld him. A stallion's life can be very solitary especially if they are not educated from an early age to behave themselves. Stallions are the most social of the sexes and struggle with isolation from other horses.
If you feel that he is special enough that you may breed from him, then there are a few things you need to be aware of.
a) You'll need to accept that he is a stallion. This means you don't punish him for having hormones - which means you need to find ways to discipline him without putting him off sex.
b) Stallions need routine and black and white rules. They are not cuddly and they are not your best friend - never trust a stallion and never turn your back on one, no matter how quiet. Most quiet stallions are so because of the above.
c) If you are going to perform with a stallion, you'll need insurance. Also, you will need to always be in attendance and your boy must always be secure. People can and will park their mares in front of your stallion's nose. Mares are your 'enemy' - they KNOW when a stallion is around and often will do their best to let HIM know they are there - very distracting for a boy.
d) At some stage you'll need to decide how to run your breeding operation. Natural paddock service is the best and provides the best results fertility wise - but the stallion and mare both need to be normally socialised for this to work. You can't train the mares (outside mares) but your job is to train your stallion to serve a mare without getting flattened.
e) If you hand serve, you'll need helmets, gloves, strong shoes and a prayer those first few times, and someone experienced holding the mare. The fine line for hand serving is between teaching a keen young stallion to respect his handler during breeding, and not ruining his sex drive.
f) good luck
