You can oberve your thoughts coming up? That means they are something happening to you, like hearing a sound or smelling a smell. Its important to remember that though we may not be able to affect what appears in our experience, we can affect how we respond to it.

If you imagine a field of grass to be your brain, your mental pathways, the more you've gone around this carousel, the more a well worn path appears in the grass, and you default to walking it. Unfortunately, the path that is worn in at the moment is there due to various factors inside and outside of your control.

Important: Be aware there are good online professional services that can assist with therapy these days - I recommend exploring them, especially if your mind goes to very dark places. You don't need to face this alone.

However, you can develop the ability to choose if you wish to engage with the thoughts that come up. This is hard, as its like choosing to walk through the grass, not on the well worn path. You will be pushing against your own habits and neurology. This is not easy, but it is worthwhile. However, with repeated regular practice, you can form a well worn path of your choosing, with more positive effects. Its not a magic bullet though, and even with experience, you'll find yourself being dragged along by thoughts sometimes, but it gets easier to haul yourself out of them.

As an example of how, there are different 'mindfulness' type meditation practices, where you 'practice' the process of observing the thoughts and letting them go. Its hard to start with, and you'll find yourself getting caught up still. But gradually you can define your own mental pathway, and more easily switch off of the negative one. Check out vippassana meditation if you need a starting point for searching, but there are many different types.

Good luck, and do also seek professional assistance (online if you need to) - having another person to bounce these things off of is super helpful.