I have never heard any member of U2 -call- another 'love,' as a name. I've heard love used as an endearing nickname (or term of affection, you know what I mean), but not by them. But then, we don't know what they do when the cameras are off.
...no, I couldn't write that paragraph with a straight face. We don't know exactly what they call each other when the cameras are off, but I'd be willing to bet what they're doing is writing songs and making music, joking around like four friends who have known each other since highschool... and not having hot gay sex. And not just because they're married, but because platonic love is not romantic love. Don't get me wrong here, romantic love can spring from platonic love. But after feckin' thirty YEARS, I think it would've happened if it was going to happen. I'd bet that what they have is so strong, it kicks the ASS of whatever lust-oriented motives would result in four-ways between them. That is to say, theoretically (and if you go way, way, WAY out of context), there could be something there, th motives don't necessarily have to be lust-oriented. But... well, I've never read these slashfics (with, I think, sufficent reasons given), so I don't necessarily know. But-- tell me if I'm wrong here-- I'll bet that if you read these 'fics with an analytical eye, the motives are almost exclusively lustful. Especially if you read between the lines-- not even necessarily the author's given motives for the bandmates to be jumping each other, but the author's motives for writing it.
(Let me make this clear, too: What you want to fantasize about in your own head is your own business. Go ahead and daydream about Larry and Bono getting it on if that's what floats your boat. But writing that? Sitting down and taking the time and the words and the altogether work to type that all out? And then putting it up in public... that's, that's a little scary, to me. If you're slashing Legolas and Aragorn, okay, whatever. It's not canon, it might be horribly written, and it's completely out of character, but they're fictional characters, so... yeah, whatever. But when you're doing that to real people? I think... maybe it's just me, the writer in me, but I think actually writing that shite down is a bad move, because physically writing it out can mess with your head. And it also makes the whatever you want to call it in your head that much stronger, and, hell, they can see it. A quick google search would show any curious member exactly what their fans think of them. Eh. Personally, my fantasies run along the lines of, ya know, writing this amazing article about some vastly important news story, covering it firsthand before anyone knew about it-- maybe busting the US President for funding anti-fair-trade attacks or something-- and getting to meet Bono, winning his approval, maybe his respect. Getting to tell him he's my hero, he is part of the reason why I am who I am. It's every bit as absurd and unlikely, it's an improbable, if not entirely impossible, fantasy. And it's a fictional story about real people. And that is why you will never see me write it down as such. Because that, in my book, would be wrong. My inner writer is the truest part of my soul. It's okay for me to have stupid fantasies in my head, in the same way that it's okay to have horrible nightmarish images, because it's just a passing thing, sometimes stuff I barely control. But to write it down? To consciously put pen to paper, fingers to keyboard, and make that vision, a fictional story about a REAL PERSON into a concrete thing... that would be a violation of my inner core, in a way... I don't know. Anyway. More than you needed to know. That's why I reacted to you mentioning that there are U2 slashfics out there by a suppressed scream, followed by laying my head on my desk for several minutes. Because that feels... wrong, in my twisted little soul, at least.)
So. WAY too much information, but to answer your question, no. No, I don't think most friends call each other 'love.' They might feel a deep love for each other, but I doubt it would be vocalised quite like that.
(Another thing, one which slipped my mind when I was talking about platonic love versus romantic love earlier, and yes, another paraphrased Lewis quote: Friends are shoulder to shoulder, they look in the same direction. Lovers are face to face, they look at each other.) Or something like that.