I have been in a relationship for about a year now. This guy seemed like a really great guy, who is caring and generous and very sensitive. Then the bomb dropped. I recently found out that he has been seeing a girl "just as friends" as he says, but lied to me about it the whole time. He completely forgot to mention her at ALL to me. Then he made up all these excuses as to why they were around each other at the time. When I caught him he said that the reason he didnt tell me is because he knew that we did NOT get along. ( I have had previous complications in another relationship with her being the other woman). He and the woman used to date casually and have been friends for many years, but she is NOT the "friend" kind of woman. I saw some pictures on the internet of the two from last weekend and they seemed a lot cozier than friends. They were both intoxicated, and he had her held very close to him with their tongues sticking out as if they were kissing through the air. He has lied several times about why they were together, the transportation they used during these times, and he deletes her number from his phone, and then locks it just in case. We have been arguing for the past few days about the situation, and he has told me that he is no longer going to speak to her, but how do I believe him? Apparently he is pretty private about their relationship as it took me over a month to find out that they were even seeing each other. We live together, and I dont see how he would be able to date her and then still have the gull to come home to me at night and act like everything is ok. I asked him if there was something wrong in our relationship where he felt he needed some other womans attention but he said that everything between us is GREAT and he just wanted to connect with an old friend. (After using the excuse that his buddy had recently broke up with his girlfriend and asked about this woman, which I found out was a lie because his buddy was not even there when they were) I dont actually know if he has cheated on me yet and I get the feeling that he hasnt, but how can I trust him not to see her anymore when obviously he is so good at hiding it?