To me, being “in love” is an impermanent, passionate, but deep feeling state. You fall in love with romantic partners, and after a while the “in love” fades away but the love (and hopefully romance) stays.
But I think you can also fall “in love” with people you wouldn’t date. There have been a couple instances where I fell in love with a female friend. Neither of us were interested in each other as a romantic partner, but many of the feelings were the same: wanting to spend a lot of time with each other, lots of laughing and giddiness, thinking of them and smiling, making lots of eager plans for present and future. Over time, like with a romantic partner, those feelings faded and now we just love each other (or, in one instance, we aren’t really friends anymore. Which of course, sometimes happens in relationships, too, once the “in love” feelings fade away and you see you’re not really compatible.)