People send out so many cords that latch onto us and suck our energy - most don't even know they do it, but a few are intentional.
There are two very important lessons to start with...
First of all, never take their crap personally. I remember when I first read The Four Agreements, that was a tough agreement for me to adopt. I blamed myself for a lot of things, when it was really the other person's issues. But I'm learning to remind myself "not my circus, not my monkeys".
The second lesson is learning to cut those cords. I had never realized the importance until just a couple months ago. Now at the end of each day I make a pair of scissors with my fingers and visualize cutting the ethereal cords that caught me throughout the day. It's not being cold or uncaring, it's a matter of self preservation. You can love someone without hauling their heavy luggage to bed with you.
Giving your love and support is completely different from allowing others to drain your life force.