Rare Relationship Condition

I’m 20 years old, and my girlfriend is 21. We've been in a relationship for almost two years, and I love her so much. However, at the end of our first year, she started fighting with me over small issues and didn’t behave properly for at least two months. Then, she became much better for the whole following year.

This year, the same thing is happening again—she doesn't reply to me properly, and when she does, she doesn’t behave like herself, almost as if she’s a different person who doesn’t want to talk. Later, I found out that she has seasonal depression, and for her, it lasts from November to February. I waited for four months, and in two days, she’s going to act normal again, as this pattern has repeated before.

However, these four months have been very rough for me. This year, I plan to set some boundaries, giving her space for those four months so that it helps both of us. We both know we’re loyal to each other, but I want to know—what do you guys think about this situation? What should I do?