Learning to set personal boundaries and navigate relationships efficiently should really be a mandatory college class.

Figure out the best way to make your friend understand that their continuous venting is causing you stress. It’s called dumping, and it should always be prefaced with something like “can I vent to you for a minute?” Asking consent allows you to decide whether you have the bandwidth to take on their stress, or not - “sorry but I’m pretty stressed myself and I just don’t have the mental energy/bandwidth right now, but I hope it gets better for you.”

Having the social awareness that they’re not just getting something off their chest, but also laying it on your shoulders, is a priceless life lesson. You owe it to yourself and the rest of civil society to teach that lesson.