Used and Dumped by my Best Friend!

We were best friends. As time passed, we decided to date each other. I was kind of into him, subtly in love with him. But when he asked for casual dating, I couldn't deny him, even though I wished for something permanent and committed. After a few dates, he observed that I was too invested in the relationship and advised me to take it casually. He also suggested that we slow things down and stop seeing each other because he knew he would never commit, and that would hurt me later. But my dumb self could not bear the loss of his absence and forced him to stay, promising that I would move on once we fell apart. A few days later, we accidentally met at his place and eventually ended up having sex. I didn’t feel like it was the wrong thing, but now that we’ve fallen apart, it has been nine months, and I’m still stuck. I am unable to move on from him. I love him so much, but he told me from the beginning that he couldn’t be in a relationship and advised me to end it. I truly, genuinely love him. I’ve been forcing this for nine months, but the relationship and friendship are getting worse day by day. I would be more than happy to have him in my life, but I can’t accept anyone else without him. How should I look at my life without him? I am physically, emotionally, and mentally attached to him. What should I look forward to? How do I accept someone else? How do I let anyone in when I let him in? If it didn’t work out, and after getting physically intimate with the person I love, I end up marrying someone else—would that be cheating? I can’t do that. If I ever have to get married, I should tell the other person about this, but I’m scared of these men out there. They will listen when it sounds good, but after some time, they will use it against us and judge our character. Am I a bad person? Am I cheating on anyone? Please suggest something and console my broken heart. Thanks in advance for your time.