Everyone's situation is hard to them, so don't feel badly about having your trucker home a lot. For a 2 year old it's still tough and so is having emotions on behalf of your kids.
Your man is out making a living - nothing heart breaking there - you have to explain it to your son that way. Daddy works just like all the rest of the world. Don't feel guilty or bad about it, it doesn't mean you son is loved any less.
And yes, tell your husband - communicate, Communicate, COMMUNICATE with the baby. Call home often, send post cards, have a special "date night" for the two of them. Bring him home treats from his route. If you and your son can put a positive spin on Dad being gone from home 2 - 3 nights a week it will help everyone deal!!
Good Luck!