Why Is It That After Rebirth, the Main Character Is His Girlfriend?

I was reborn, yes, with the memories of my previous life when I was 25 years old, and the system. I felt that I could rely on the system, get into a good university, accumulate a lot of wealth, cure my girlfriend's illness, and live a happy life. Just when I was imagining a bright future, I strangely discovered that my girlfriend's health was gradually getting better, and the company she founded continued to expand, but my system was unexpectedly useless. It seemed that the protagonist of the script was not me, but...