Active Sex drive

I very confused now, I have a relationship and i have a very high active sex drive but when my partner goes to work when he is not around with me, I tend to think about having sex with other guys at my workplace or outside. Is there any problem with me? Like having such fantasy or problem? I still do have sex with my partner regularly. I have to masterbate 2-3times a day if there is no sex, sometimes in the toilet at work. I don know who to consult so i will just post it here to ask around if anybody experience the same as me. I am very afraid thats why i keep this from my partner and i don't know what if he finds out if i had affair with other guys. I tried to do it lesser but sometimes i just couldn't control. I also tried watching porn and masterbate to control the urge, but the more i control, the more I will end up having sex outside and the more guilty i feel. What should I do?