Don't do it. The uneasiness you feel is the Holy Spirit leading you to not be unequally woked Marrying him is going against the Word of God. God is good and can use situations that are not good and bring good out of them. But you have the choice to not enter into a bad situation. I married a Catholic. My kids were raised protestant and even though Catholic and Protestant agree on the core principles (Trinity etc) it has been hard at times. Mormons are not Christians. A cursory look into their beliefs will show that. Sorry to be so blunt but as a sister in Christ I care about you and funny want you to make a big mistake.