There is only one way: take that first step in faith.Remember what happened to the people of Israel when they had to cross the Jordan in order to enter the promised land? Well, when the priests, who carried the Ark of the Covenant, dipped their feet into the water, the waters parted and they, together with all the people, walked through on dry ground. Don't think those priests were not scared. They were but they trusted God and by faith in him remembered all the wonderful things he had done in their lives.
So you too, in order to leave behind a sinful relationship, God expects of you that you take the first step and... the rest will follow.