P.M.
Many kids are simply not neurologically or emotionally mature enough to complete potty training until they are three, or sometimes older. Boys tend to train later than girls, and age 3.5 is not uncommon. Toddlers often simply don't recognize the signals until it's too late – their is so much going on in their little worlds that's more interesting. Even if you can coax children to train earlier than their natural inclinations, kids get overwhelmed by looming parental urgency and expectations, or the simple size of the commitment, and regression or prolonged training is more the rule than the exception.
Allowed to proceed at their own speed, kids show interest when they are ready without urging, or even surprise their parents by announcing when they know they are ready. And then they are. Children WANT to train when they are ready, just as they WANT to walk and talk when they are ready.
Comparing your son to your daughter will only become a source of unhappiness for you both. Your little guy sounds like he's getting there, but your eagerness is thwarting you both. Putting him in diapers won't confuse him if you tell him you trust him to learn to use the potty when he's ready. He will appreciate your trust in his ability to grow up just right.