Sometimes people withhold the truth because they don’t want to hurt the other person. But it depends on what truth exactly you’re referring to. Are you able to give us some examples? As for not living up to promises that in itself isn’t necessarily an indication that he will cheat, just that he couldn’t keep site of his goals.

My ex husband cheated. Signs? He would outright lie about where he was and what he was doing. He became very secretive. Passcode locks on every single one of his devices. Going out random hours. Text messages during the evening. Wedding ring suddenly fell off in the swimming pool but I found it in the car. I could give so many examples here and yes it sucks if you’ve been through it in the past.