What to say to boyfriend of six months who recently broke up with me due to stressful situation???

My boyfriend is really stressed out right now because he is changing jobs, having severe financial troubles, and just got kicked out of where he was living. I didn't realize how stressed out and overwhelmed he was feeling until two weeks ago when we had a big fight and he broke up with me. He said he is so stressed out right now that he can't deal with tryign to have a relationship and make me happy too. I got mad and yelled at him and he said he is sorry ~ he thought we could work it out but he realizes now we can't. We haven't spoken since and he leaves next week to go away for a month and train for his new job. I feel like enough time has gone by and I would like to make contact and let him know I am thinking about him. I don't know if I should apologize for not being more understanding and tell him I woudl like to work things out when he comes back or not mention the break-up and just wish him luck with his training. (I thought an email would be best.)