DO you think my boyfriend cheated on me? please read, please.?

my bf got back from working abroad 2months ago, he was away for 6 months. he's the type that would never cheat, and wants to marry me soon :) however i knew something was happening then between him and a girl. after asking him to tell me the truth (when he was still away) he said she kissed him 3months before when she was drunk and he was planning on telling me when he was back. i got very upset as it hurt..and he was still hanging out with her and doing things together (running, bungee jumping etc). then after he got back and she emailed him saying stuff like if he's going to ignore her she'll tell me everything. i added her blah blah she told me that they never kissed drunk, and it was just easy to say to me. and that i shouldnt trust him anymore...he said its not true and got very upset and annoyed at her. he emailed her but she kept sticking to her story, then when i looked at their emailed he said things like 'i told u we couldnt talk when im back as she would see our emails blah blah blah blah' and she said like 'domtn treat me like some hoe u can have sex with and then forget about' blah blah. i got annoyed nad questioned it, he said he only said it as he thought she would leave us alone then. however emailes after that he deleted before i saw them.he promised on everyone life nothing happened. since then (2months) shes blocked from our fb, and emails and we have no contact with her. however i keep thinking that i trust him but i think something did happen. i want to add her on fb and ask..or am i being stupid?

together for over 2years, he's planning on proposing soon :)