How do you get a man to be sincere?
By not pointing fingers.
What do you need to ask?
Not the "you trust me?" or "do you really love me?" because that will tell him to back off.
Make dinner, light some candles. Make him feel like you care about him first and foremost. Talk to him about your day, your week, how much you think about him. Eventually he will feel comfortable enough to talk about it. If he says or does something you can't really tolerate, don't explode right there. Apologize and leave (or make him leave if it is your house). But be sincere: If he hurts you, let him know. Also let him know you WANT to work things out. That is, if you really want to.
The base of a good long-term relationship are the three Ts: Trust, Think and Talk. Trust him and make him trust you. Think before you talk. And lastly, Talk. Talk talk talk talk and talk. And more talk. And more. A relationship is formed by two people, and even if you know that person a hell lot, you won't ever know 100% what he may be thinking of. So ask, and answer. but don't point fingers! Remember the Trust.
Good luck!
-Jean.