I Am In Love With Someone That Battles Depression, and Anxiety

It's hard some days, other days are great...Sometimes I get frustrated. I get upset at my self, at my thoughs...I keep them to my self, because I enjoy the good days so much. What can I do to help? This all sucks. It's been over a year, he wasn't like this at all...I get it. Ive been there. I wish I could do more.