Hey Caroline
How long is his apprenticeship?
It sounds to me that...well...you are love sick. I am not a therapist or anything...I am just a person who suffers from depression so take what I say with a grain of salt. But yeah...your feelings seem very normal to me. You are grieving him not being around. You miss him. I think the feelings of numbness are just a way to protect yourself. But as you say...when you are with him again...the feelings all come back.
If you seriously do think you are showing signs of a clinical depression as in a great change in eating and sleeping habits, loss of energy, etc...maybe get an appointment with a therapist.
In the meantime I think you just gotta find ways to cope when your boyfriend is away. Is there something which can keep your mind busy until he returns?
Hang in there. Please write back to tell us what happens with your story.