Some of the people on this thread replied that your friend probably isn't as happy as she seems (which is likely true), and some people said you will make yourself miserable by comparing yourself to others, which is also true as far as it goes.

But both of those responses can miss something, which is to offer insight and compassion into this core pain you having, the pain of depression. Even if your "friend" is really absolutely miserable, that doesn't help you much, because you still feel the acute pain of depression. And for a depressed person to suffer because they see happy people everywhere is pretty normal. It's not the cause, it's the symptom. The pain of the depression is the most primary thing, and making all these comparisons happens on top of that.

So it's a priority for you to put yourself in a situation where you can feel cared for by yourself or others, and give that depression a chance to heal.

Also, see if you can get in contact with the pain of depression as something separate from the thoughts it creates. See if you notice sensations in your body. If you notice your thinking, see if you can notice the tone of voice it comes in (does your thinking sound like a depressed person speaking?) and how the tone of voice affects you.

For a person in a serious depressed state, who is used to making comparisons and does it automatically, it's likely too much to ask them to stop comparing themselves to happy people, but if you can be more mindful about the root feeling of depression, and more mindful of the tone of voice the thoughts come in, then you will feel less gripped by the depression. Hopefully you can feel a sense of increased freedom to choose what you want to think about, or choose what you want to do.

Think of the depression as a sickness, and love and compassion as nutrients that can help you regain strength. Do what you can to put yourself in situations where you feel love, compassion and empathy.

Mike