My rant for week ending 5/7/2010.....I am so confused.

My husband and I have been married for 4 years and have been together for 10 years. He has cheated on me before when we were younger and I forgave him because we have 2 kids together. Plus, we were young and I thought it was something he needed to get out of his system. So, I stuck by him through it all and forgave him. However, you never forget something like that. After all these years, I have learned to trust him again and our relationship has gotten better. Well, at least, I thought it was. We have a roommate that has been a family friend for as long as I can remember. I was messing around with her phone last night, not being nosey, but just checking it out. I found a text message on there from my husband that pertained to them being intimate. I asked him about it and he says he sent it playing around. I looked at his phone, which I haven’t done in like 3 or 4 years because I had no reason to, and all his messages had been erased since the 6th. I really get suspicious and I then ask our roommate about it, she said she never seen the message. The day the message was sent she was out with a guy friend and she thinks maybe her guy friend seen it and responded. I don’t really no. I am not sure I believe it entirely. But I truly believe that our roommate wouldn’t do that to me. We have been friends forever. It doesn’t stop me from believing that my husband would still try to sleep with her. After we discuss all that and I am just so mad and hurt that I just drop it. I started looking at our phone bill to see if maybe, just maybe, there was a way to see what the messages said that were sent. I notice on the bill that there is an unknown number on there. At least it was unknown to me. I asked my husband about it and he said it was a girl that works at the store up the road from us that took one of our puppies. I also noticed that they were texting at almost 1 am in the morning. I asked him what was up with that and he said that the puppy was sick and they were texting about the puppy. Then I noticed that they were texting all afternoon yesterday. He again said it was about the puppy. I asked him why all the texts were erased from his phone and he said because he knew I would blow it out of proportion and jump to conclusions so he deleted them. I told him if they were really talking about the puppy there would have been no reason for me to over react. But he erased the messages and it makes me think-what is he trying to hide. Now I am at this point that I can’t trust him and I hate feeling that way. I don’t know what to do. Should I believe and look the other way or should I go with my gut and leave?