This is not a good idea. If it backfires, you could breakup.
Here are the risks:
?You become obsessed with him
?He leaves you
?Bad luck, long term
Plus, it just isn't that moral. If you don't believe your boyfriend is telling the truth, talk to him. Remember, spells are powerful, but if you communicate, you can fix the problem with no risks at all.
Maybe he wants to cast a truth spell on you? How would you react to that. If you found out he casted a truth spell on you, you'd probably break up, because it shows that you don't trust each other. Just talk it out.