How to deal with ending engagement/relationship

I'm at my breaking point and I need to cancel my wedding and end this relationship. We were supposed to be getting married July 7 this year wich would have been our 4 year anniversary, but due to my fiance's lack of responsibility in all aspects in his life I refuse to keep being a mother to him. Im 24 and have 2 kids, I don't need to be raising someone a year older then myself.the last straw is him quitting his job while currently 5k in credit card debt (and I only learned about the debt a few months ago). What's your advice for leaving this relationship? We rent a house together, we share a 18 month old daughter (my other kid is from a previous relationship) I've completely falling out of love with him I haven't let him touch me in weeks I can't even say I love you back when he tries to say it. But this is still hard having to start over with 2 kids now and I'm worried because he's threatened to keep my daughter from me. How do I leave this situation?