How to get rid of, guilt?

I’ve been best friends with a girl for almost six years, she means the absolute world to me. But a month ago, we had our first fight. The year before she was dating a guy for a little over a year… When they finally broke up, he was heart broken but she moved on to another. The boy was very depressed and eventually came to me for help. After about a month he came clean about having feelings for me. I had a very small crush on him as well, but I was also trying to work things out with my ex. When my best friend found out that he had feelings for me, she begged me not to talk to him. I promised, but I just kept talking to him in secret because I felt bad & in a way, I was using him to get over my ex. One day I ran into him at the mall and we went to see a movie. I made out with him. Now I completely stopped talking to him, because I can’t tell my best friend; I would loose her if she found out. Recently, I did work things out with myy ex. But the guilt is eating me from the inside out. My ex, now boy friend doesn’t like the kid. my best friend would disown me.. And now the guy I made out with feels so worthless because I used him… I guess coming clean seems like the way to get rid of the guilt. But if I do, I loose everything. Is there any way I can drop a little of the guilt with out loosing my best friend and boy friend??

Thank you,<3