Technically, unrequited means to pay back or pay up, so you can have an unrequited service where you pay for or solicit a service but it is never fulfilled, but you seldom hear it used with anything other than love. 

Capt. Susan Ivanova:
[Sitting on the floor in Medlab, rocking herself back and forth, crying silently and staring at Marcus's body] I said go away!

Dr. Stephen Franklin:
Susan it's me. You okay?

Capt. Susan Ivanova:
Damnit Stephen, why the hell did he do it?I didn't want him to, I never, *never* would have asked him to!

Dr. Stephen Franklin:
I know. [he sits down next to her] I know.

Capt. Susan Ivanova:
And how the hell did he find out about that machine?

Dr. Stephen Franklin:
Look, after we gained control of the Alien Healing Device, Sheridan and I decided it was too dangerous to let others know about it, so I coded all my log entries. He must've hacked his way through half a dozen security overrides.

Capt. Susan Ivanova:
It's typical, he was always pulling crap that like, even I never knew what the hell to do with him. He was the most undisciplined, the most annoying... [glances back at his body] I was just lying there and I was feeling myself letting go of my body. And I remember the last thing I thought was, 'I'm gonna die now'... and it wasn't so bad. And then I heard this voice coming from far away saying 'I love you.' And I thought 'Is this God? Is this God?' I mean, he really did have an English accent just like in all those old movies. And then I felt myself being pulled down, and I got heavy, so heavy, you know, tired, and it was... I forced my eyes open, and there he was next to me. And we were hooked into that damn machine, and I tried to pull it apart, Stephen, I swear to God I tried. I just-I couldn't even move, I couldn't move! [breaks down sobbing]

Dr. Stephen Franklin:
Look, there was nothing that you could have done, all right? Your system was traumatized. You can't blame yourself.

Capt. Susan Ivanova:
I don't, I don't, I don't. I just-you know, all my life I've had problems with relationships. You may have noticed.

Dr. Stephen Franklin:
A little.

Capt. Susan Ivanova:
You know, the ones I loved always ended up hurting me or leaving me. And the ones who stayed, they had nothing inside. No depth. After awhile I just decided to forget about it. And then, here was Marcus. I knew he'd never hurt me... and I knew that he'd never leave me... and I knew that he loved me. I knew it. I just didn't want to admit it. And he gave so much, and he wanted so little in return. He just wanted a kind word, or a smile and all I ever gave him in two years was grief! It's because I think I saw what I wanted. And I was afraid.

Dr. Stephen Franklin:
I thought you knew it wasn't going to work out. You were just protecting yourself from being hurt again, that's all.

Capt. Susan Ivanova:
Maybe, but maybe I should've tried just one more time. I could've done that for him. Now I can't. At least I should have just boffed him once.

Dr. Stephen Franklin:
'Boffed'? Did you just say 'boffed'?

Capt. Susan Ivanova:
[managing a weak smile through her tears] It's the type of thing he would've said. I mean hell, it's not like I was doing anything else.

Dr. Stephen Franklin:
Well I guess that's one way to deal with unrequited love, huh?

Capt. Susan Ivanova:
All love is unrequited, Stephen. All of it. [She leans towards Stephen and he gathers her in his arms, both of them now crying softly]

From Babylon 5 S4E21 Rising Star