I know it's really difficult to be in a relationship with someone whose levels of desire have waned. Even if you know that it's due to depression, it's hard not to take it personally and feel lonely. I know you don't want to add to your boyfriend's bad feelings, but I'm not sure that you should be keeping this all to yourself. IMO, it's important for him to know how you're feeling, and maybe together you can come up with some ideas about
different things you can share with each other. Of course you want to be supportive to your boyfriend, but you also need to deal with your own feelings, too. Depression affects both partners, and you may want to get some counseling or other form of support for yourself to help you to cope.
Living one day at a time.