How can I(18m) tell if I’ve fallen out of love with my girlfriend (19f) or if it’s just depression?

We’ve been dating online for over a year. Things started off great, but over time, I began sinking into depression and started feeling emotionally detached.

There was a period when the depression lifted for a few weeks. During that time, I felt genuinely happy; I wanted to be close to her and was deeply in love with her. But after those few weeks, the depression returned, bringing emotional emptiness along with it.

Now I’m confused and don’t understand what I really feel for her. Rationally, I know we’re a good match and there are plenty of reasons why I should love her, but on an emotional level, I feel almost nothing right now.

How can I distinguish between actually losing romantic feelings and the emotional detachment caused by depression?

It’s also probably worth mentioning that this is my first relationship.