First Love Syndrome
The first person you truly fall in love with. You want to spend every moment with this person, you're almost addicted. You picture yourself marrying this person. Even when things turn sour, you're sure you'll work them out. Even when you break up, you're sure that after some time, even in the future, you will get back together and live happily ever after. Because you love each other, how could you not? This usually happens in your teens. And when you mature more, you (hopefully) realize that it was just first love syndrome.
Wow, Jill really thinks she is going to get back together with Jack after he dumped her on her birthday? She just has first love syndrome.
First Love Syndrome
A blind love for a person because they were your first, where you ignore any problems and think you'll be happy forever. Until you're not.
You so had first love syndrome for her/him