Love can happen with anyone and at anytime, no one can change it. U can love more than one person at a time. But i think its morally wrong. You are not doing justice with your partner or i would say partners.You are not comitted, and are cheating  Think if the partners you love also loves you and some one else, how would you feel?

and in the 1st place why would you look for someone else if you  are  in a relationship? If you are not satisfied or out of love for some reason,why wouldn't you just break up and start a new relationship with someone else?

But there are always exceptions.