In a number of cases, the Supreme Court has ruled that "mere breach of promise to marry" is not an actionable wrong. Let me discuss the case of Wassmer vs. Velez (G.R. No. L-20089, December 26, 1964). Wassmer and Velez were sweethearts. They decided to get married. Thus, they applied for a marriage license. Invitations were printed and distributed to relatives, friends, and acquaintances. Wedding dress for the bride-to-be and other apparels were purchased. Dresses for the maid of honor and flower girl were prepared. Matrimonial bed with accessories were bought. However, two days before the wedding, Velez simply left a note stating "will have to postpone wedding - my mother opposes it." One day before the wedding, Velez advised Wassmer "nothing changed rest assured returning soon". However, Velez never returned and was never heard from again. This prompted Wassmer to sue Velez for damages. The trial court found Velez liable for damages. On appeal, the Supreme Court sustained the award of damages. Although MERE BREACH OF PROMISE TO MARRY is not actionable, the award of damages in this case is justified under Article 21 of the Civil Code which states that, "Any person who wilfully causes loss or injury to another in a manner that is contrary to morals, good customs or public policy shall compensate the latter for damage." In other words, Velez was held liable for damages not because of his breach of promise to marry but rather due to his unjustified action of allowing all the preparation and publicity of the wedding only to walk out of it before the marriage is solemnized. The Supreme Court found his action contrary to good customs.
Going now to your question, my opinion is that the Contract of Unity and Engagement cannot have any force and effect. Let us say that you and your boyfriend signed a Contract of Unity and Engagement wherein it is stated that the parties agree to marry each other. After signing it, you decide that your boyfriend is not the right person for you. Can your boyfriend sue you because you changed your mind to marry him in violation of your Contract? The answer is NO because the Contract partakes of the nature of a promise to marry. The only difference is that the promise to marry was made in writing. As you know, mere breach of promise to marry is not actionable. This is true whether the promise to marry was made verbally or in writing.
Furthermore, a Contract to that effect can be struck down for being contrary to law, good customs and public policy. Under the Family Code, one of the essential requisites of a valid marriage is that consent must be freely given. If a party to a marriage agrees to be married because he/she is bound by such a Contract, it cannot be said that he/she is freely and voluntarily giving consent to the marriage. Furthermore, the Family Code defines marriage as the foundation of the family and an inviolable social institution whose nature, consequences, and incidents are governed by law and not subject to stipulation.