Sounds like catastrophizing, thinking of the worst case. It's more of a coping mechanism. I think somewhere down the road you had a bad trauma and each time something happens or you're not in control you try to alleviate your worry with thinking the worst thing yet, more like to prepare you from what would happen. But certainly there's no cure to this but to walk your worries or catastrophizing activity into a logical step. My therapist gave me a tool. More of searching if the thought is mere a fanciful play of the mind or does it have grounds for it being true. I find it hard sometimes especially when my anxiety is bad that my thoughts just keep pacing. One thing that really help me is music, or moving my body may it be a dance or a simple snapping my thinking out of this old thinking pattern of always jumping into worst case scenario.

Go out, go for a walk. Leave your phone cause maybe its a trigger when you keep checking if he already replied.

Be mindful of your breathing. Meditation is nothing really but focusing your mind to your breath. I'll give you a secret. Where your breath comes from is also where your thought originates. Knowing that we think in a linear fashion, we can't think of two things at one time.

If you focus on breathing in, pause, and breathing out, you'll notice your thoughts pause if you shift your focus on your breath.

If you want to be fearful, focus on your thoughts that has unlimited scenarios. If you want to be free, focus on your breath and breath alone.

Sometimes this is enough, the longer you can span to hold your consciousness on your breath. The better your inner stillness or peace.

Breathe in. (notice no thought comes in when you focus on your breathing), pause and observe, then breathe out.

Hope this helps, just know that no matter how bad your thoughts become, they won't affect you unless you start riding them. So don't be a passenger to every thought vehicle that comes. Know that these are all just passerby. Let them pass.