AITA for asking my friend to stop venting to me

I would say in general i am a very good listener and someone who always makes space for people to open up to me about personal struggles or feelings they are having. In most friendships this is normal and goes both ways. Being support systems to each other. Recently a good friend of mine i have known for some time has began non stop “trauma dumping” on me, almost making me feel like their personal therapist. It sounds harsh but let me explain. We have always been super vulnerable and open with each other. We would be good support systems for each other. In the last few months it’s gone from healthy support to treating me like my sole purpose is emotional supporter and less like a friend/human. i can understand this friend and i feel for them because i know they are going through a hard time. it gets to a point though when our only topic of conversation is negative and about their problems. we don’t talk about much else. i rarely am able to talk about myself. whenever i talk about good things going on in my life, they get frustrated and have even asked me to not talk about these types of things because it upsets them. there have also been several times i wont hear from them for days and ill get a random call to vent to me and then thats all the conversation is. any time i would try to suggest fun plans to cheer them up, they would get upset with me. it felt like not sitting in the feeling with them and also being miserable myself frustrated them. then this friend began calling or texting out of nowhere asking me to meet up with them to talk, but they expected me to drop everything i was doing to make time for them to once again vent to me and use me as their stress release. if i couldn’t because i was busy or already had plans, they would sometimes lash out at me, get angry, or guilt trip me. i dont want to feel like im just someone therapist or emotional support. i also have a lot of personal things going on and dont always have the mental capacity or energy to carry the weight of my friends problems as well. any time i try to express these things and set boundaries im not met with much understanding or kindness..these are things that have been happening consistently for months. it honestly leaves me feeling drained when our friendship feels one sided consists of nothing but negativity. i ended up asking for time apart and asked that our only interactions stop being about these topics because it is starting to affect me. does it make me a bad friend for no longer being able to make space for this? i’m wondering if i went about things the wrong way and came off a bit harsh