Those three words—"I love you"—can be the scariest set of words in the English language, and yet we tend to say them all the time. If you're not sure you should be saying them to somebody, then you've come to the right place.
If your first reaction is "Self, what kind of question is that? Of course I love him/ her!", then you're on the right track. Similarly, if your first reaction is more along the lines of "Um, well, it's complicated.", then hold off on saying the words. You might just be "in like," or perhaps "in lust." Both have their places, but they're not love. .