First of all, there aren't really "easy spells." Either way, you need to know what you are doing and have a solid understanding of spell casting before you do any spell.
Second of all, you don't know for a fact that he is cheating. You are assuming it, which will get you no where. Ask him why he's being distant, or blantantly ask him if he is cheating. You have to have an actual conversation with him to know what is going on. Sit down with him, and say what has been on your mind and ask him what's been on his mind. After that, you can figure out what to do.