First of all, make sure you don't say anything that you won't keep. If you do, and you don't keep your word to it, who knows what he might do.
Promise him you'll never put him through what his ex put him through, and ask what you can do to help him get over the feeling of being cheated on. Try to always be positive and nice to him, don't put him down in any way.
Simply, the best way to do this, is to treat him with a lot of respect, like how you would treat your best friend. Have a nice long talk with him, promise to tell the truth all the way, ask anything he'd like.
Personally, I wouldn't trust him as you can't rely on him.
No move on
Look, if you cheated, the trust will not be above an 80% point for years. A relationship really has to have good foundations to keep going if one has cheated. If there is no cheating, then trust shouldn't be a factor and he is being silly. I would say cheating can be considered hanging out with another guy/gal without purposefully communicating it to your partner.
No, unless you really believe you can make things right again...
No.
Humans can simply make mistakes and cheating on a partner is a big mistake. The bond of trust is broken between the two people and it is difficult for the partner who has been cheated on to ever trust their partner again and it is difficult for the partner who cheated to earn that trust back. If you feel your partner is a flirt; it has happened before then it is wiser to walk away, but if you feel it is the first time this has happened then you should sit down and communicate your feelings to your partner and that you will not stand by and be used while he cheats and ask him to be a man and tell you the truth. Then you will have to make up your mind from there.
You first must find out if the trust between the two of you is workable, and base your decision on that.
Rebuilding trust is one of the hardest things in a relationship. If your partner has accepted the fact that you've cheated and most likely forgives you, that's a sign that the trust will build back up faster than normal. However, if your partner doubts and questions your loyalness to him, make sure to do little things to make him trust you once again.
you will have to earn the trust back and it will always be harder for him because he wont know if you will do it again.
To believe in him requires you to trust with your heart. But if in your heart you believe otherwise, follow your instinct.
Just give your ex-partner some time. If you truly have not cheated, then when he has had a break, try to meet up somewhere neutral but public, like a shopping centre, and try to explain to him what really happened. If somebody is spreading rumours, use friends to help find the source and get the person to admit they lied. If you have truly cheated, then the relationship is over. Cheating on someone who trusted you with their life and gave you the ownership of their heart is one of the worst forms of betrayal human beings can commit. It will take time, it won't happen by magic.
It'll take them some time, but they should eventually. Depends on how strong your relationship is.