Kayzr I am sorry that you are going through this.
Trust has to be earned. It is not an automatic right just because you are in a relationship.
So it is going to take time.
And it will need him to do things that demonstrate to you that he can be trusted. He can't "just do nothing". He has to be there when he says he will be, be where he says is, let you see his phone, let you see his emails etc.
He has to actively demonstrate that he can be trusted.
Only you can decide how many times he has to do that, or how long it will take. It is an individual thing.
One thing you must remember though, is that if you take him back and tell him you forgive him/trust him now, then it must be true. You cannot take him back and not believe in what you are saying and still have doubts.
That is not fair on you, or the DCs.
In that respect this is actually more about you than him