My fiance calls his ex very often, and doesn't want me to know

First of all, we are long distance relationship, he moved to Wisconsin, and both his ex and I are living in bay area.

Now back to the topic: He called her often recently, and deleted the records from his cell phone so left nothing that could show he called his ex-wife when I visit him.

His explanation was: she was depressed and he was trying to help her. I knew his ex-wife had some problems, and I never stopped him to discuss the issues with her. But why did he hide all of these from me, and lie to me? I even asked him few times: "did you call your ex-wife? how's her problem now?" The answer was: "no, I didn't call her."

I always thought that we were crystal to each other, we talked about everything that happened daily, and I trusted him 100%. Now he kept calling her for months long, and he never mentioned it with even a word to me! I felt so unsafe because I never knew that he could hide things so deeply from me, and I don't know what else he could do behind me.

I can not trust him as much as before. He started to lie to me, and I don't know how to handle this. I need your kind advices.

I only see two possibilities: Either he doesn't trust that he can be open with you without you freaking out, or he is still emotionally involved with her.

What is the nature of her problem, how long ago did they break up, and how long was their relationship? Do they have kids? What sort of relationship do the two of you have? Are you slightly jealous or suspicious by nature?

You're driving him back to her. Stop acting like a threatened little brat and realize that they broke up for a reason. Maybe she's trying to get him back by playing the "poor me" card, but do you think you're helping your own case by acting all wounded about it?

He lies because you make him lie.

sounds peculiar to me.

say to him that bothers you not when he speaks to her, and ask to not hide this from you, because that will make things hard.

I'm wondering how you know he called her? If he says no, and there's no record, I have trouble seeing the evidence. Help me out here.