Does anything become binding upon me if I deny the existence of previous relationships before marriage and swear to that effect, intending dissimulation (tawriyah), out of fear that the marriage will not be completed?

You did well by not informing your fiancé about your sin from which you repented, for a servant, when they sin, should conceal their sin and not expose themselves. There is no blame upon you for swearing to him, denying your involvement in the disobedience, using equivocation (tawriyah) to conceal yourself. This is because denying a sin to conceal oneself is permissible, otherwise, the person would be openly proclaiming their sin.