You said:

"Your muscles can become accustomed to the workouts. It is like when you first start running the first few weeks are really had. Then you get accustomed to the distance as the muscles build and adapt. As the muscles grow they also take the stress off of other muscle fibers as they share the load."

I agree with what you said, except in his case he never gets the soreness. It doesn't matter what muscles he decides to work on or how much strain he wants to work with. He never even got it when he first started getting into weights again. As with me, it is the opposite. I can work out on an excercise and feel the soreness for about 2 days and do the exact same exercise the next week and get the same soreness again. But I do make gains in my body doing it.

It could also be that he has higher endorphin levels. This is common with people that do intense exercise. The endorphins kill pain, so the soreness can be there and you will not notice it. When I use to race triathlons and do cross country bicycling I did very intense daily workouts and almost never got sore. One time I had to be somewhere in two days that was 300 miles away. So I loaded up my bicycle and did 200 miles the first day through the desert and mountains. Got up the next day and did the final 100 miles to my destination. I was never sore the following days. I know part of this was from being accustomed to long days and the extra weight on the bike as I went everywhere on by bike and carried everything I needed on it. But it was also the endorphins that helped a lot. In fact if I had to rest from injuries I would actually start to get withdrawal symptoms. So I would often continue racing and training when sick or injured. In fact my favorite trophy was the one I got for last place I won in a half marathon I ran when I had a cold and strep throat. I really felt like dying through the whole race but I finished. Endorphins are also released by many drugs, and are substituted for by narcotic pain killers. They can do a great job of masking pain, and they can be very addictive just like the narcotic pain killers.

Because the excess epinephrine (adrenaline) contributes to the nervousness. If his adrenals are being taxed more he will not put out as much epinephrine as you.

You say that their adrenaline is shot. The funny thing is that my boyfriend never gets the tension that I can get from drinking coffee.

Again, lack of epinephrine.

He is always really relaxed. Also, he has so much more energy than me. He can get up a four thiry am and go to work from 6am to 4pm or later, and then go work out and get 4 or 5 hours sleep, while that is impossible for me. Even on the weekends he gets up at 5am and is not grumpy. I just don't get it. And he is diabetic and still has more energy than me.

For one, some people can naturally get by on less sleep. I have known people that have always gotten by on 3 to 4 hours of sleep a night. Everyone's system is different. Then there are also other factors that affect energy levels. Thyroid function is one. And women tend to be a lot more prone to hypothyroidism than men. So this could be a factor. Liver function is a factor. Diet is a factor. Red blood cell levels and function are a factor. How we utilize our fats will play a role. Again people who do radical exercise will have systems that will spare glycogen and burn fat more efficiently, which is the best fuel source for the body. They also utilize oxygen more efficiently. So his higher energy levels could be from a number of things.