Why does it happen? I can only guess - that these people like how they feel in your energy and want more. Think of it like a drug. And it's human nature to manipulate the information for their own benefit. Wish I could say differently, but there are few...and I mean very, very few folks who will be able to separate their own desires from any truth in a situation.
Trust your gut. do what you feel is best for you and your own sense of honor. It is a lonely path when you walk it with integrity. Even fellow empaths will subconsciously try to control things. We're stuck in these vessels. You really have to take on some heavy self-awareness to side-step all the mess.
If you can use these moments to help those trying to use you to get them to see what they're doing, maybe that's part of the path. Most won't want to see the truth of their behavior, so be prepared for some ill-received behavior on their parts. But, one never knows if being a mirror might help another soul take a step forward.
Peace to you.