boyfriend problems

Hey ladies I need some advice I'm to sad and mad at the same time and I don't know what to do! So me and my boyfriend have been together for a year and he cheated on me in September but I forgave him, alothogh I forgave him I still had  some trust issues but we worked through it. Today one of my girlfriends sent me a picture of what her friend sent her and the picture was a screen shot of her friend talking to some girl she knows. And while they were having this whole chat she asked my boyfriend if he had a girlfriend and he Straight up said he didn't. Is that wrong for me to get upset? And I'm that kind of girl who completely respects my other half and I would never even respond if some guy was trying to flirt. Anyways long Story short he completely denied it and said  that I'm "full of it". Ugh! Let me tell you, being a red head that didnt not help keep my temper! But please please give me some advice!