Talking out stress=good, but there's a difference between someone who just needs that healthy sort of support and someone who just dumps all of their shit on your shoulders and does nothing to fix it by him- or herself.

For example: "I'm so suicidal. I just want to end it all, my life isn't worth living. You're the only good thing in my life and the only person I can talk to"
"Hey that sounds heavy, and way above my paygrade, maybe you should seek professional help"
"Nah I'll just keep dumping it on you, and you alone (because you are a girl and this is what girls are for, right) making you the sole person I rely on for my mental health. You will then feel responsible for me and keep trying to help, while I have no intention of actually trying to get better"

That is exhausting. And not all that uncommon.