Yeah, for the same reason that you missed her... because you lived with it for so long

Rob:

You don't look at the things that you have, you only look at the stuff that you don't have. Those guys are right about you - you're money. Mike:
Then why won't she call? Rob:
She won't call because you left. she's got her own life to deal with, man, and that's in New York... alright? And she's a sweet girl, and I love her to pieces, but fuck her, man. You gotta get on with your life. You gotta let go of the past. And Mikey, when you do, I'm telling you: the future is beautiful, alright? Look out the window. It's sunny every day here. It's like manifest destiny. Don't tell me we didn't make it. We made it! We are here. And everything that is past is prologued to this. All of the shit that didn't kill us is only - you know, all that shit. You're gonna get over it. Mike:
How did you get over it? I mean, how long did it take? Rob:
Sometimes it still hurts. You know how it is, man. It's like, you wake up every day and it hurts a little bit less, and then you wake up one day and it doesn't hurt at all. And the funny thing is, is that, this is kinda wierd, but It's like, It's like you almost miss that pain. Mike:
You miss the pain? Rob:
Yeah, for the same reason that you missed her... because you lived with it for so long