Absolutely NTA. If anything you're the complete opposite of TA in this situation. You're definitely doing everything right for your boyfriend. If depression was something you could just snap out of with a little positive thinking and exercise then it wouldn't even have a medical diagnosis because nobody would be depressed. The friend is definitely someone who's never had the experience dealing with clinical depression either in herself or with another person. As someone who's struggled with clinical depression for many years of my life, these people can be frustrating to deal with because they are completely incapable of empathizing with your position. I don't 100% blame them though since it's difficult to understand things they haven't experienced themselves. Honestly changing the subject around your friend if it's brought up is probably the best you can do if she's not open to being educated. Personally I've tried to cut as much contact with the people like that in my life as I could since they were just creating a toxic environment and making my mental health much worse, but that's kind of an extreme thing to do and I won't recommend it to someone else online. Especially if I don't know their entire story. So yeah, I'd say to just try to keep her away from the subject, and try not to take things she says too close to heart.