How can i get over him if he is always around

Hi i'm 23 Years of age, i was in relationship for 3 years not were living in the same roof, we have plans for our future, we even establish everything. we have house , settled everything.
but all of it was gone, i was working in one of the company here in the Philippines, i was assigned in the office. their was an office mate of mine that at the very first i don't really like him, he is tall fair complexion, bit handsome but i can deny that he got a gut. but every thing turn to a feeling that i really don't want.
May this year when we become close, we talk, i told him even my intimate moment with my another ex before my present boyfriend, time run soo fast. we get close, we watch movies, we dinner together, while in the company we are always together. then July this year everything that was kept in us suddenly burst. we had a dinner late night my boyfriend was at night shift while i'm fix in the morning shift. we had a beer after dinner, then he brought me home and all things that i really don't want to do happen.
we had sex that night July 12 this year. i regretted it but with out knowing i still did those thing with him. that night was the start of our relationship. but the worst thing is that he has a live in partner for 4 years, in short were both in relationship.
their was the time that he broke up with his gf because of me when my bf was not at home he is the one who slept over. but if not i'm the one who slept at their home. i never expected that from enemy we become that close that sweet. August this year that was my dad birthday so i have to go to our province for 5 days. at first we have a constant communication we got Skype messenger and every thing that is available to keep our communication. when i come back i think theirs something wrong thats why i asked him, nd i was right, he had sex with his ex. my world fall apart. i come back with my ex. then he is keep in courting me but i neglect him. then their was a time i confronted him. i came at his house without knowing that his ex is already their ( who happened to his gf, in short he two time me.) i slap him. after that we meet at the office but as usual we treated each other as sweet as we our. i admitted my bf and i was together all those time. we both betray each other, but i know deep in my heart i love him i dont love my live in partner.
but i'm a practical type my live in partner have more stable job, his income is bigger that my office mate soo i kept my office mate chase after me. until that time came he was tired of chasing me he broke up with me. we came back with his ex ( now they are living together again) my world fell apart when i knew it. i regreted everything.
now My live in partner already knew what happened to us. but he still forgive me. we planned our marriage July next year. but deep inside of me i still love my office mate but how can i win him back to patched things up?? our partners love us soo much, but i know that we still have this feeling that someday we will be together.
i really regretted i chose money over happiness and love. How can i move on?? if he is their always around.
and i know marrying him is not a solution. :(
im badly in pain now i need some advice