Blessings and welcome.
I was wondering if you two were planning on having children? and I was wondering if she has maybe some hormonal inbalances too, or pain that she struggles with?
I think you should return to school as you had dreamed; you obviously married to share your life with her. I'd have a talk with her and tell her you dream of going back to school to do ___ to better your lives together. Tell her you are devoted to her and she and yourself are your NO 2 priority in life. Ask her if that would bother her. I believe you can still be there for her. Giving up your own dreams could cause her more depression. Maybe she needs to feel more needed and more "connected". Try "connecting" with her more. Make time each day JUST for her. Tell her how much you love her. Ask her if she would like to do a special class together, etc.
She needs you yes, but you needing her gives her purpose too; purpose I believe gives our lives meaning.
I live with chronic pain and I have thought a lot about universal suffering: physical, emotional, psychological, social etc...and it's tough to be wrestling demons daily.
I hope I have not sounded callous. I pray your wife finds her way out of her darkness, my mother has lived with depression for 46 years but she's STILL HERE! she lives as if God has a purpose for her life. ALSO "When we go outside of self it's where we FIND OUR TRUE JOY and meaning" help her find that...
You are a devoted husband.