How do I make up with my boyfriend after an argument?

My boyfriend and I got into an argument before we left college for the summer. We both talked about things that we need to work on about ourselves. We ended up leaving on good terms, hugged, and left. He told me that we need to stay in contact over the summer so our relationship doesn't die. I agree with him, I have been working on the things that he brought up and I am getting better. But he has been ignoring everything that I send him (texts, facebook messages, so I stopped sending them for a while to give him space), and now I am just hurt and confused. It has been three weeks since we last spoke, and I do give him a little leniency because he has been working a lot and he and his family are currently on a huge family vacation. So I don't want to pester him, and I cannot stand conflict. But I really want to speak with him because I miss him terribly and I want to know what is going on and let him know that I still care about him a lot and miss him. I have some people telling me to dump him, and others telling me to wait it out, he will turn around once he gets back. I just have no idea, and I am afraid that I will screw this up horribly cause I don't want this to end. His birthday is in a few days, and I am sending him a card, only I am still figuring out what message to write in it because I want to tell him some things and tell him that I want to come see him sometime, but I also don't want to appear needy, worrisome, I just need to add something simple that brings my point across. Any help is much appreciated! And sorry if this was a long read...brownie points for reading it all the way through!