What do you advise me to do, as I proposed to a girl and then broke off the engagement for a trivial reason, which harmed her and her mother psychologically, and when I regretted it and returned to propose to her a second time, her father refused and swore he would not marry her to me, and I feel great guilt?

The engagement is a promise of marriage. It is commendable to fulfill it, permissible to break it for a valid reason, and disliked without justification. You have done well by attempting to re-engage the girl, but you are not obligated to anything, nor is there any sin upon you, since her father has rejected your proposal.