Hi L.,
I'm confused about what he thinks is so hard, and I truly don't mean in any way to belittle his situation. He's taking a full load of classes and working part time? Is that it or are there other factors that he is dealing with? Most college students work part time while they take a full load of classes. part of what college does is teach you how to manage the things that you are responsible for... school, work, family, friends, distractions etc.... how to plan your time and prioritize your behavior.
I feel a little bit like you may be setting him up to fail again. If you tell him that it won't be like this forever..... well, when it IS like this forever (and it might or might not be) he will be disillusioned again.
If he thinks that this is the hardest it will get he is going to be in for another rude awakening when he hits middle age if there is another economic crisis, or the woman he marries has health issues or, god forbid, something happens to one of his kids or he has to start all over with just the clothes on his back because of a tornado or earthquake or hurricane.
Instead of sugar coating life for him.... can you instill that he can do it- whatever "it" is and whenever he has to do "it". He needs self-confidence so that whatever life throws at him he can get on top of it and make the most of it.
His life might work out. I know people (some on this site) who put in the hard work, made good decisions, used "elbow grease" and built a life that by the time they were 30 had it all worked out.
But most people - especially in this economy - have seen their 401K depleted, are trying to make a mortgage payment on 1 salary instead of the 2 they had when they bought their house and are trying to figure out how to re-build their life and keep their head above water.
So telling him that if he puts in the work now he will have an easy go of it... isn't the direction I would take.
Tell him to take care to choose a career that he loves, because he may have to do it until he's 80. Tell him to choose his friends and his girlfriends wisely because they are the people who will help him reap the benefits of his hard work. Tell him you're sorry he had the mistaken belief that being an adult = freedom and that being an adult means taking care of others and providing for the ones that you love. Instill in him a sense of responsibility to work to build a life and a family rather than equating work to a payoff that will buy him materialistic wealth and an easy ride down the line. He needs to understand that there are no guarantees in life, but that no matter whatever happens he is a strong man and he can figure it out because he has the basics... intelligence, tenacity, drive, motivation, desire. not because he worked hard at 20 to buy an ipod or put gas in his car.... but because he is a hard worker and will work to build his life.
Good Luck