I don’t know what to do ..

I have no one to talk to so I just came here . I’m actually devastated . I don’t know what to do . So there is this guy that I love so very much and I did everything for him . Paid the rent when he didn’t have the money , gave him a full tank of gas to get where he needed to be even when I barely had enough money for myself , and the list goes on . We’ve been messing with each other for 3 almost 4 years but I’ve known him my whole life . He lives with me and my mom and he has to pay rent to her but she sees him as like her son . I love this man . But he always tells me that he can’t trust me because of something that happened freshman year . During freshman year his friend come over to my house at night and asked to play the game because he had asked my mom before and she had said yea . So I said yea and opened the door and let him in . WE DIDN’T DO ANYTHING I was in my room and he was in the living room and 2 hours later I hear a knock on the door and it’s him and he comes up to me and tells me that he’ll keep our secret safe . I was confused because I was in my room the whole time and it was eventually found out that his friend came over to have sex with me when me and this dude was on a break . But he keeps holding me to that .. that’s his reason why he doesn’t trust me . Even tho I’ve told him the truth countless of times . He just won’t believe me . But anyway last night I was at work and my phone is currently broke so he came to my job and asked what time I got off so that he can pick me up , I didn’t know what time I got off so I told him I would just walk but he said no and insisted that I take his phone so that I have a way to call him and tell him I’m off work . I did and I finally got off and I go on his phone ( I let him have friends because he always tell me that it’s not like that and he sees girls as his homies) and I see him texting one of his girl friends I wasn’t to worried but then I read something that caught my eye when I was trying to get out of the messages .. it was this big paragraph of how much he likes her and he likes that way she carries herself and he likes the way they cuddle and she holds him tight and he likes the way that they fuck ... I am completely devastated .. I put so much trust and love in him even when he showed me that I shouldn’t .. he keeps saying that since I’m not a guy I don’t understand that it was just “busting a nut” but that’s not what this is about .. it’s about how he lied and acted like everything was fine .. it’s about the principle of the situation . And now he’s threatening to leave so he’s packing his bags and is gonna move out . I don’t know what to do .. should I have not even read those text messages ? Is this somehow my fault ? I don’t want him to leave .. I’m going to be alone .. I hate being alone .. he was the only person that made me happy .. the only thing that mattered to me . I love him so much through all his tough times and through all of his insecurities he’s my angel . I’ve always made him a priority he always came first and now I’m completely lost .. I don’t know what to do .