I am still suspecting he is lying to me?

I confronted him about flirting with a younger single lady (over text message) I felt he lied to me over a number of days so yes I snooped, should not have but i did. 3000 messages saved from her, she has a nick name he called her o sweet one, my cyber woman, and when she asked about any hot dates or hot chicks he deleted his answer. Previous to this he always told that they banter back and forth and she is just a pen pal. (They met the same time as he met me we were regs in a chat room) A couple of texts from him was him (as he put it) playing with her to have her call him. Oh she does not know he has a gf that he lives with (we have been together nearly 2 years). Well it was blantant flirting the texts i did read. So anyway post confrontation .... I was told I could not threaten someone with leaving to make them do something you want them to do...(now take into consideration I dont care he is friends with her I am asking him to tell her about the fact he is in a committeed relationship). I was also told they are playing. And he can't stay with an emotionally weak woman. Well you can image trust has been broken really on both sides, me because I went into his personal space and him because he has lied to me about his intent with this woman. I am finding it very hard to look at him and have any form of respect for him or trust. We left our conversation that he would tell her the next time she texts. Well its been a week and a bit and we have not discussed it. His behaviour has chnaged towards me he knows that i confided in my closest friend about the situation and yesterday i accidently text him instead of her, i was just saying that his attitude has changed and i have been sitting here wondering how i can get the trust and respect back when it occurred to me that its not up to me. He came home and said oh you text me accidently today. I said i did? he showed me text and I was OH im sorry did not mean to and I wondered why Cory had not replied. He said do you feel embarred now? I said no why should I? what is done is done i cant undo it. He asked how I could mistakenly text him instead of her? I said well im so used to texting you I have been doing it for over 2 years now, i guess i just was not thinking im sorry. He said I think you are full of ****....I let it go.....Its 4am in the morning and i have access to his phone and im very tempted to look ....... would you? Since our confrontation i still feel he is lying to me. I have the option of leaving on April 20th and im seriously considering taking it. So please answer the quesiton would you check on him?