When you are trying to decide if the pressure to be monogamous is to blame, you have to take in account outside people, not just a cheater`s point of view.
Not ALL monogamous people or those who live monogamously will disown you. Not all monogamous people will preach 'their way' into your ear.
You will find acceptance from some mono folks.
Odds are, you will have mixed reactions. Some will put you down for your choices, some will tell you it`s your own life, and others will just be happy for you.
If monogamy was to 'blame' then you absolutely wouldn`t have a choice, to be who you are. The truth is, you always have a choice. Some people may have better options then others, but there is always a choice, even at a basic level.
Cheating is always a self-centered decision. There are many 'reasons' to cheat. Sometimes people have the right to be selfish, or feel they need to be. That is a different subject though.