Hi there. First off, are you speaking to a therapist? ERP (exposure response prevention) therapy can be extremely effective for something like this.
Regardless, what you want to do is demonstrate to yourself that it's okay to be home alone, and do so at a very slow and gradual pace that is reasonable for you.
The key word here is "demonstrate." You won't get very far by thinking your way out of being afraid, because the parts of your brain responsible for making you feel fear while alone don't understand language, they understand experiences.
This means that you're going to need to do some things that go against your thoughts, which might seem terrifying at first, but once you prove to yourself that it's not as bad as you think, it will become easier. This is one of the basic premises of ERP therapy.
Ideally you would navigate this with the help of a therapist. If that's not possible, then I can tell you what I would do; just keep in mind that I'm not a professional and I don't know you, so take this with a grain of salt.
Start by having your son stand outside for 5 minutes, leaving you alone in the house. During that time, you will likely experience some anxiety and intrusive thoughts, and that's okay. Simply notice the thoughts, and be aware of how your body feels, even if it's all very uncomfortable. Don't try to get rid of the thoughts, but don't latch onto them either. Just acknowledge them, and allow them to come and go like storm clouds passing through the sky.
Instead of focusing on the thoughts, focus on your body, and notice the symptoms of anxiety that you feel. Again, you don't have to do anything to get rid of the anxiety, just notice what it feels like. Think to yourself, "pounding heart, tight chest, tense shoulders," or whatever else you notice.
Whenever you find yourself getting lost in the train of thoughts, just gently bring your attention back to your body. Even if this happens 1000 times during those 5 minutes, just keep doing it. Every time you move your attention away from your thoughts, you're strengthening the ability to ground yourself into the present moment.
Maybe try doing this once every day, until you notice yourself feeling less triggered by the idea of being alone for 5 minutes. Then, bump it up to 10 minutes, then 30 minutes, then maybe 45 minutes...you get the idea. Pick an amount of time that is just outside of your comfort zone.
If you do this properly, you will retrain yourself to not get so triggered by being alone in the first place. As that happens, all of these intrusive thoughts about what may or may not happen while you're alone won't bother you as much, and will happen less often because you don't pay them much mind.
Hope some of this is helpful!
