I think this song is about being able to love someone enough to let them go. It's the right thing to do - "You know that I cannot stay," but it's still difficult - so she doesn't want him to "come around" right now. It's hard for her to take, and she can't pretend it doesn't hurt. After all, while she says she's happy anyway, she still wonders if he'll miss her - "those arms that used to go around you" (a la No Questions Asked, a song about Lindsey leaving her behind). I think she would like to be missed - wouldn't we all? But he's gone for good, and this realization makes her sad.
The love she feels for him is "very powerful," so that a piece of it still survives, even though he "cannot stay." Even after he's left he still has power over her. But she know "all about love" - and if he "cannot stay", she needs to let him go. So she does, and though it makes her sad, she does it without resentment or anger. She can still be happy, and they can still love each other - just in a different way. This is a very mature view - and one that she no doubt takes with Lindsey now.
The interesting thing about Love Is is that it was the first song written for the album, even before Stevie's fateful conversation with Tom Petty. While it does seem to fit where Lindsey and Stevie's relationship is likely to be now, it must either have been a premonition or about someone else entirely!
From the moment that I heard this I fell in love with this song and really get the sense that it is a conversation between two people that are firstly dealing with the initial stages about love,Stevie may be asking, "Do you know what Love is?" and the other person is answering, "No I don't, but whatever this is.. its very powerful."
The beautiful and endearing words that are often spoken. "You've got the softest lips" But something has happened and it all ends. but somehow they are reconnected and those feelings are again brought to the surface.But they have both accepted and moved on. "Love is watching you go" the old saying if you love somebody set them free if they come back they are yours if not then they never were.
I think this is a conversation her and Lindsey had before he left
Fleetwood Mac in 87'. I think they were together intimately one last time and this is the conversation they had afterwards. So when Lindsey left she just broke down emotionally coming to the realization that he is really gone.