I used to be extremely sensitive to my own emotions and others' as well. I am very aware of the energy in group dynamics and one on one. For example, I just started working and on the third day, my boss seemed a bit more stressed than usual and I thought it was my fault. I started being worried that I did something wrong, until I realized what I was doing and told myself to stop, immediately. No use spending time thinking about a remote, vague possibility when I could focus on the here and now, on what I am doing and what I have to do and when a problem comes, I will deal with it (with time) but I can't solve a problem that is not actually a problem yet. I focus very much on what I can actually do.
I have learned to have very 'localized compassion', very specific ones and with support from Te. If I can't do anything about it, I tell myself that it makes no sense (absolutely none) to feel terrible, to make myself feel terrible because no one else is responsible for my emotional state more than I. So I ask myself, why would I willingly make myself feel terrible? Over something I can't change no matter what I do? This isn't a complete thought. If I let myself feel bad over every natural disaster that happens, bad as in I spend hours crying for the missing and the dead, then I wouldn't be able to do anything else.
Did I feel bad about Haiti? Yes. Bad enough to cry for more than two minutes? No. Could I do something about it now aside from giving money? Realistically, no. Does it make sense to keep feeling bad and be less productive/functional? No. Does it somehow inspire me to keep going on my human rights major/infrastructure/development/politics track? Yes.
If I am with a friend. If she feels bad, I try to give good advice, give compliments, say what I think. Sometimes my goal is to make her feel better with 'sweet' things, sometimes I get her to laugh, and sometimes I am blunt and lay out her options. I actually feel bad about myself sometimes more than the person having the problem because somehow, this is really messed up, I place myself in their shoes and feel that their situation is a possibility for me and they are handling it badly so I will handle it badly and that her X equals my X and her Y my Y and ... *explodes* Not so much that I feel bad for her.
If it's a minor negative emotional vibe and not an outright conversation about my friend's situation, I will ask if she is okay, but I wouldn't necessarily feel so bad myself. I may feel that the connection is weaker on that particular day so I leave her be and do my own thing. And when she is ready to talk, I am there for her. Maybe this is a difference between INFPs and ENFPs? The introversion may make it easier for us to keep boundaries while ENFPs strive on others' so it is natural that they'd be unable to separate from the negatives when they enjoy the positive emotional sharing so much.
I totally agree with Scott's two posts.