The primary objective of marriage in Islam is guarding one's chastity by saving him or her from committing fornication and fulfilling the desire to have offspring. This objective cannot be fulfilled except through sexual intercourse; so, for a man to stipulate such a condition is simply wrong and unacceptable. Furthermore, it is also a clear case of spousal abuse as it entails dereliction of one's duties towards his partner. The Prophet (peace be upon him) said, "Your spouse has rights." Sexual intercourse is one of the fundamental rights which neither a husband, nor a wife can afford to neglect. If either one does it, it amounts to a serious breach of the terms of the marriage contract.
It is best for you to decide to terminate this engagement now that you have not solemnized the marriage yet, rather than ending up in a relationship which is simply unnatural and unjust. Otherwise, you end up leading a married life, in which you will find no fulfillment, whatsoever. I pray to Allah to inspire you to make the right the decision and save you from an abusive marriage.