There's a term in the psych world called an "Energy Vampire." It's actually used quite often in random convos with certain intellects. Even Oprah did a full segment on the topic of these leeches that go after a person's good character and intentions for manipulative purposes.
What is an Energy Vampire?
If you've never heard of the phrase, an Energy Vampire is someone who literally just sucks the positive, lively, optimistic and good natured energy right out of ya whenever you are in their presence.
The relationship starts off good, of course. You may find a common ground to be pals or more, but then, it's like they turn into an alternate of themselve