What about in the case of parent-child relationships? Is a parent's love for them conditional, or is it unconditional/"pitiful?"
Well, in the style of unconditional love that makes sense to me:
Even when a child has done heinous things, and even when the parents are furious with their child and abhors what they have done, I still have empathy for parents who do not abandon their kids and continue to interact with them even if I think said child should be punished to the fullest extent of the law. That's just parental, unconditional love to me. Momma visits death row, even if she can't stand what her kid has done, because she still loves her child? I respect that. Those bonds don't break.
Other relationships, as people have said (such as romantic ones between equals), i don't think unconditional love has a place... or at least it just comes down to not treating someone as less than human; certain relationships need to have equal contributions from both parties in order to grow and thrive, rather than one party being willing to accept anything the other party does. I think it's possible to forgive a partner who has wronged you, while still drawing that relationship to a close in the way it had existed.
^ i often wonder about this because i don't have any kids of my own (yet?). what happens after children reach adolescence and the feedback turns negative, though?
You ride it out, steady as it goes.
Typically there's just a bad stretch, usually caused by the process of breaking away from the parent(s) and becoming more independent, and then the relationship mends again just with new parameters.
But yes, it can be difficult, painful, confusing, and exhausting if you have a bad run with one of your kids. Sometimes it comes down to remembering that you are the parent and your child is not an adult yet, so you need to be the adult and not look for affirmation from your child; get it from a peer.