I'd suggest for that situation not doubting yourself by accepting that you do doubt yourself. There's nothing wrong with doubting yourself. Accept it then you can release it. Change it around a bit. Just say to yourself, "I doubt this will happen." And then say to yourself. "Which is exactly why it will happen. To prove that my doubt is unfounded. The universe is going to prove me wrong and ___ will return." Will being the most important. Because it will happen. As long as it's something we want (prefer to happen, not desperate to have happen), the Universe will give it.
Also do as Veronica suggests. Ask what if. What if they call you? What if they come back? What if your doubts aren't worth having? What if your doubts don't stop it from happening? What if they want you more than you want them? What if they are thinking of you right now?