I want to move on!

I have a boyfriend, we have been in relationship for 10 years now. Last year we argued because he hide our relationship in *** to flirt with other girls. After that I decided to ask for seperation with him for a while to see if we still want to come back together later or not but we were not break up properly. While I was in seperation with my boyfriend, I have talked with one guy his name is Zim, we have know each other for 3 months. I told him all about my relationship and we were starting to flirt each other more than friend. Our relationship was so good, he took care of me and care of me on everything. I was so happy whenever we talked and talking with him can make me slowly forget my boyfriend. One day my boyfriend came back and begging for my forgiveness. He asked me to take back out relationship in ***, he willing to do everything to get me back to him and sorry for what he have done. Me and my boyfriend we have a business together which is our commitment that hard to break up, also our families are friends and our families never know about our argument and they planned to form up our wedding next year. The crazy thing I did is I accepted his apologize and get back to my boyfriend because I was too afraid to lose everything we have together. I told Zim everything and explained everything to him. He seem to understand and accept everything, but it did hurt two of us alot. In that night we talked all night and cried before change our relationship to be normal friends. Saddly after I get back to my boyfriend, I don't feel like I love my boyfriend anymore. I keep on missing Zim everytime. No matter how good my boyfriend treat me I can't feel passionate like before. I did messaged Zim and told him how I feel to him but he act cold and detached me. He treat me like a stranger, he has no concern about me like before. I even asked him if I'm not in relationships with my boyfriend anymore, can we back together? He answered "it's too late now I can't treat you the same way anymore" I feel so bad and try to accept it but I can't. Now I don't know what to do with my feeling I'm so struggle. I'm in relationship with my boyfriend but I keep on missing Zim all the time. Even I want to go back to Zim, he will not open minded to me anymore. Can you lead me the way ? What should I do ?