Can you be in love with someone you know you might not be with for the rest of your life?

Like, you understand there is a possibilty that things between you and your partner might fall apart, you hope not, but it’s pretty much inevitable. Is what you feel still love?
I’m curious cos a friend of mine said to me that she was in love with this kid but that they probably won’t last. Is this just her being negative about relationships? Or is she just being sensible? Or is what she feels for this kid really not love?

And also, is it always better to keep in mind, when getting into a relationhship, that things might not work out? Or is it seriously best to believe you’ll be together forever no matter what?