Praise be to Allaah.
Allaah concluded His Message to mankind with the religion of Islam, and He tells us that He will not accept any religion other than that. Allaah says (interpretation of the meaning):
“And whoever seeks a religion other than Islam, it will never be accepted of him, and in the Hereafter he will be one of the losers”
[Aal ‘Imraan 3:85]
Your backing away from the religion of Islam is considered to be a loss for you, and a loss of the happiness that awaited you, had you entered Islam. You should hasten to enter Islam, and beware of delaying, for that delay may lead to regrettable consequences.
With regard to what you mention about the reason for your backing off being the idea of plural marriage [polygamy or polygyny], we will present to you the ruling on plural marriage in Islam, and then the wisdom and noble purposes behind it.