I have to agree with the other posters. listen to your instincts, and to me because I was in almost the same situation. Your gut is telling you something, mine was too but I ignored it and ended up with a broken heart. I snooped through his phone, which is a behavior I am not proud of, but I needed the truth and I found it, and it was too late. I think if a man has nothing to hide and is in love with a woman, bringing up your suspicions or asking to see his phone wont blow up into him being defensive and not speaking to you. But, if you are always snooping for no reason or questioning him when he is tellig you there is nothing (which I dont think you are), then that is an issue on your end. From what you are saying, his behavior is shady from the onset- why not tell this woman he has a GF- he is protecting her when he should be protecting YOU! Be VERY VERY careful and vigilant.