It is an extremely tough situation to be in - that point when you realise that the solemn vows that you gave your partner (i.e. to be monogamous, forsaking all others) just isn't the way you feel any more.
There are some folks who are lucky enough to have a partner who, when the bring up the subject, is willing and able to deal with it - the marriage vows and contract is "renegotiated". There are, however, quite a few marriages that fail because their partners don't want to embrace poly and the poly person sees loving more than one as something that they can not or are not willing to put aside.
I wish you luck.
"Listen, or your tongue will make you deaf." - Native American Proverb