When paying it forward is paying too much

Like most reasonably charitable people, I've always believed in "paying it forward" even before the book and  movie  made the concept famous and it got its own foundation. But lately, I have wondered how to draw the line between doing the right thing for others, while still leaving time and energy for my family and myself. A homeless couple approaching me for a place to stay prompted the reevaluation.  Since the woman was pregnant, I felt like I was turning away the Virgin Mary and the baby Jesus.  But, my fear of a bedbug infestation, and a sense that the couple weren't what they seemed, stayed my natural generosity. (The last place they had stayed supposedly had bedbugs, and I was very aware of how easily the little bugs transfer from clothing and belongings to new digs - in this case, my house.) So I didn't invite the questionable homeless couple to bunk at my house.  Despite her apparent pregnancy, and their cute little dog, I decided to trust my con-meter, and walk away.

But all the way home, I felt guilty, despicable, and low. Was I inherently selfish?
Later, as I discussed it with a friend, we developed a long list of all the people who I support emotionally and physically.  Perhaps, I had taken "paying it forward" a bit too far.  Lately, I have been struggling with exhaustion, in part from a sense that I never had time to do the things that really mattered to me.  After reviewing my schedule, it turned out that I was trying to support more people and activities than was possible for me -- at least if I wanted to have any energy left for my own projects.  So, I reviewed my commitments, evaluated where I really felt I was making a contribution (the English as a second language classes I teach, for example) and the situations that were draining, but didn't seem to appreciably improve the world.  After that analysis, I cut some charitable activities out of my schedule (for example:  shoveling horse manure out of the corral did help the horses, but it took an hour to get there and an hour to get back back, and I was physically exhausted afterwards.) 

 Even though I've trimmed my planned activities, I will continue to try and brighten salesclerks days with some light friendly banter and a smile.  And I'll happily petsit for my neighbors, or share my cookies with my elderly neighbor who loves cookies but doesn't bake. And I left a core group of "pay it forward" activities in my schedule.  I don't want to stop saving the world, but I want to save myself as well.