Everyone is different, so I can´t say for anyone else, but even if a friendship is very very important to me, I am unable to express that emotion effectively, so I don´t. Some of the most important things that people have said to me, or done for me, I have never let them know. But, if he is lonely, and is struggling socially, its a good bet he does appreciate it.
You´ll know if he doesn´t want to be your friend when he doesn´t return your calls, or refuses to meet with you completely(when it just happens sometimes this could just mean that he wants to be alone, we tend to need that A LOT, so a random dispersal of instances where he ignores you probably only means he needs some alone time, if he agrees to meet up with you later, then this is probably the case). But I think that you can only infer that appreciates you indirectly, cause he probably won´t say it. But, if he always agrees to meet with you and go along with your plans, its the best indirect indication that he appreciates what you´re doing.
All I can say is that I wish that I had more people like you in my life who would make the extreme effort it would take to hang out with me, because I am not capable of doing it, and I am sure a lot of the other people here agree.