Love doesn’t distinguishes things and people. It is an energy that just flows. Any attempt to control, change, resist and manipulate Love will only result in fear, hatred and guilt.
In certain cultures marriage and strict rules surrounding this institution can become a barrier to experience Love deeply. There is nothing wrong with being in Love with many people at a same time but just that certain cultures, relegions or society do not allow this.
But these rules and beliefs are false and do not promote Love and harmony. So you can be yourself and accept things the way they are.