People often make the mistake of assuming magic is a cure all for every sort of problem, they often only turn to magic for romantic reasons such as this, when said problem is most easily solved by talking and not magic. The reason why magic is not ideal for relationship quick fixes is because this often involves making one party go against their original will. You should not make somebody go against their will and I highly disregard it.
What is most beneficial for you would be to talk to him. Understand that from his point of view it would seem as if you are going back to him as a back-up relationship or one out of pity, so the fact the he is iffy about the relationship sais that perhaps you should sit down and have a nice long conversation like every other couple does. I suggest you explain to him that your reasons for choosing to give this other male a second chance was your decision at the time and in no way reflects back to him, also that you realized that you want to be with HIM, not this other guy. Mostly though, just reaffirm the reasons why you are with him, and the reasons that you did not give him the immediate second-chance. If you really want him to forgive you, put patience and love into the relationship, put yourself in his shoes, and talk. Compromise and talking and dedication are what all healthy relationship are made out of, there is absolutely no need for magic, and it would only make the situation worse. Magic is not the ultimate relationship fix-it and often only makes things worse.