Welcome to the world of heartaches and heartbreaks. I have been there. It hurts a lot more when they leave without a trace and more when they give us no reason.
You were cheated. No doubt about that. Acknowledge this first. You are the victim here and to imagine you are going through all this along with your cancer is devastating. I pray to God that your pain lessens as soon as possible. The first thing that you must do right now is to seek answers to the questions that are haunting you. Getting convinced is the only way out. Trust me, it took me more than 5 years to get the answers I sought when I was going through a heartbreak. So the sooner you find answers to these the better it is for you. I can help you here – only if you tell me what those questions are. Another way is to pray and communicate with your God. Write letters to God – start journaling. Let the pain flow out of your body. Drink more water to cleanse yourself. Develop self-love. Seeking love in another person always leads to pain. Hence we should love ourselves more than we love anyone else.