You should get him to a therapist. There's a good chance he is suffering from Post-Traumatic Stress Disorder (PTSD), which is common after a serious accident or other life-threatening event or psychological trauma.
Depression is just one of the many symptoms (see links below) of the condition, which is commonly associated with combat veterans, although it can affect anyone. I went through it myself after a serious auto accident in 1999, one in which I should have -- and would have -- died had two good Samaritans not pulled me from my burning car (I was unconscious). In the weeks and months following my accident, not only was I depressed like your boyfriend, but I also felt anxious, irritable, off-balance and guilty. It took time, therapy and lots of support from my family and friends before I got back to my happy-go-smart-ass self.
My point? Two, actually: 1) the condition is real; 2) it can be successfully treated. You can try lifting your guy's spirits all you want -- I'm sure it helps -- but he needs professional help, especially if he's never discussed the accident and his feelings about it with someone who has the skills and experience to help him. Encourage him to seek treatment, and be patient with him; it sounds like you already are, which is great. I'd also encourage him to read about PTSD, as the first step to beating your problem is understanding it.
Good luck.
More information about PTSD:
Cary is right about your boyfriend needing therapy. A month and a half ago, I was in a car wreck that broke my back in 6 places. I don't know exactly what your boyfriend went through, but I can understand some of the reasons why he is probably depressed...
Having physical limitations when you previously had none is incredibly frustrating and at some times humiliating. Imagine never being able to bend down to pick something up that you dropped, and having to have someone constantly pick up after you. Or not being able to shower by yourself, requiring someone to be in there handing you your shampoo and not even being bake to towel yourself off on your own. All you want is to be ablento go about your daily mundane activities without the constant reminder that you're an invalid and can't really take care of yourself... It is SO depressing.
He is lucky to have you there for him, but he might still feel lonely despite having your support, if he isn't dealing with his emotions about the trauma he has gone through on a deep level. The anxiety and frustration of being in a cloud of limitations, and not having someone around who really knows what he is going through, can lead to him bottling up his deeper feelings. Physical trauma is something that affects a person on an intense emotional level, and that needs to be taken care of too.
Also, his painkillers may also be contributing to the depression... I have found that getting massages and going to acupuncture, as well as trying to be on as few medications as possible, helps combat such chemical influences. He should try visiting a pain management specialist to see if there are more effective ways of handling his pain so that maybe some of the depressive narcotics he is on (if he is on any) can be eliminated or lessened.
OMG, Cary and Britannia - so glad you both came through your accidents and that you are both still with us today.
Seeking professional help is so helpful. It doesn't have the stigma it used to, or that it is a sign of weakness. While I did not go through physical trauma from an accident, I did realize I needed help when I went through a really bad series of events. In Nov. 2007 I lost my beloved long-term job, in April '08 my husband had his first affair, in June '08 I lost my mom after being her caregiver for a few years, in Sept. '08 my husband had his second affair and then asked for a divorce, and in Dec. '08 he spent Christmas week with his favorite girlfriend (he tried to hide both affairs from me). I call it my year of loss - lost my job, lost my mom, lost my husband, lost my home and lost my pets.
I was finding it hard to keep a grip sometimes (I'm normally so even-keel). The counselor I saw helped me so much, and I was riding a wave of positive energy after just a few sessions. I also learned who my real friends were when I needed to talk to someone who knew me and were there for me when I went through some low times. The anonymous asker is great for caring for her boyfriend and wanting to help him - he needs you more than he knows. I wish the best for you both.
He was in auto accident too, he was hit by a drunk driver. He was a photographer and he went into a comma after the accident. His business went into a bankrupt and he's now recovering from various serious health conditions. It takes a toll on our relationship, he constantly feels there would be no future for us. And that, above all, throws him into deeper depression. Thank you Cary, Britannia and Mags, for sharing.