I want to take temptation away!!! Is it wrong?

My fella slept with a girl when things were complicated between us last august. I've asked him manus a time to break contact with her altogether, he said he would and then texted her. I gave up and said fine whatever but just even tell me in passing that you were texting or talking to her so I don't get paranoid and think you're cheating on me. He agreed. Last night he was out and I waited up for him (the friends he was out with usually end up that drunk that he comes home in a right state and I didn't want my daughter being woken up) I went on to bed about an hour after he got home as I have work this morning, he sat up for about an hour after. I didn't get to sleep until he came to bed cos of his music playing(our rooms next to the kitchen) anyway long story short, I heard him talking to someone, immediately thought of this girl as he wouldve texted her when he was drunk. This morning I did the unthinkable and went through his phone to find that she had texted him saying sorry she had fallen asleep while they were on the phone!!! Plus he's topped up his phone, where he got the � from I don't know cos he's not working at the minute and I gave him the � to go out last night. I've a chance today of taking his phone and getting rid of it. Should I? Or should I wait and see if he tells me that he was talking to her??? Please help me someone!!!! I know he sounds like a loser but he really isn't, there's just been alot of complicated things happening this last year.