AITA for checking my girlfriends phone to see if she was cheating on me?

I (21m) met my gf (20f) at a party and we started seeing each other. Over time she became my girlfriend and it’s been a great four months. After four months, I introduced her to my sister and later on to the rest of my family. My sister didn't like her but my parents did. After four months my gf Wendy asked me to meet her parents. I did and they seemed to also like me. They were happy that we were together. After this, we decided to move in together. We rented a place together and things have been good. I work from home as a freelance writer and my girlfriend works the night shift in a bar.<br><br>I’m your average guy but I never had a girlfriend before so I never took my sister’s advice on how to date a girl seriously. However, after dating Wendy I learned that I should have. My sister told me to search the girls name that you date online to see if anything bad pops up. She said this as a joke but it stuck with me and after I met Wendy, I did as my sister suggested. I searched Wendy’s name in multiple search engines and nothing bad came up.<br><br>I was looking at what other things I could search in her name. So I searched "Wendy [Lastname]Hotmail" and it showed her email. I clicked on the link and it took me to her email account. My sister used to always say “A girl never leaves her email logged in” but she was wrong. Wendy’s email was logged in. I returned to the search page and searched for Wendy’s name and linkedin. I saw her linkedin and clicked. It took me to her account. I thought the same thing, "A girl never leaves her social accounts logged in" but Wendy’s account was logged in. You don’t have to explain to you how I got into her other accounts, but what I do need to explain is that I saw a message from another guy in her established connections.<br><br>The message was from December 2020, 3 months before I met Wendy. It was a message from a guy named Sammy and it said "So you want to do it?". Her reply was "Yeah, I want to meet you". I wasn't sure if this was before we met or not. They both only had first names on their accounts. I searched for "Samuel [Lastname]" on linkedin and it popped up nothing. I searched "Sammy [Lastname]" and nothing came up. I then proceeded to look into other social accounts. I saw she had one email where she emailed a guy named Samuel. His email was [email protected]. So I went to his rocketmail account and it was logged in. I looked through his emails and saw that he emailed my gf (Wendy) in February 2023. <br><br>I opened the image and it was a picture of a guy. Who I dont know if its Samuel, but it was definitely a guy. I searched her phone. I opened her phone and saw that she had a message from Sammy. I opened the conversation and it was from December 2020. She said hi to him when the conversation started and he said hi back. I looked and their last messages were also in February 2023. I downloaded a screenshot of the messages and sent them to myself. I then sent the messages to my sister. She called me and asked me if I confronted my gf yet. I said no and she said I need to confront her immediately. <br><br>I told her I'm not going to confront her because I need to go to therapy and tell them I invaded her privacy. My sister was angry and said I can’t tell them I invaded her privacy and not that I was checking to see if she was cheating on me. I said I wasn’t going to tell them the real reason and she said fine but "make sure you get rid of that bitch". I was crying because I really loved Wendy and I didn't want to think negative about her. I left the therapy appointment and went home. I saw Wendy getting ready for work and I hugged her. I told her I love her and she said she loves me too. I went and laid down in bed. I was crying a bit and my gf came up to me and asked if something was wrong. I told her I was okay and went to sleep. <br><br>I ended up not telling my gf that I searched her phone because I was afraid of the reaction she would have. She did get suspicious that I was hiding something because I was always asleep during the night and I was awake during the day. I saw one of her texts and it said "Hey Wendy. Who is this?". It was a text from an unknown number. I looked at her texts some more and I found a text from another unknown number. "Hey Wendy, up?". I’m beginning to get a little annoyed that I found two texts from unknown numbers sending messages of “Hey Wendy, up?". She had been acting very nice the past few days so I decided to forget about it. <br><br>Wendy went to work on Saturday. I went to the bar that she works at and I sat in the corner. I watched Wendy take some orders and then she looked at her phone. After 10 minutes of her looking at her phone a guy walks in. He sits down and Wendy goes to him first. She takes his order and then goes to take other orders. After a few minutes she goes back to the guy she took the order from first. She’s been with him for a few minutes and I see her hug him. The guy said something to her and she shook her head and walked away. After 20 minutes the guy that Wendy hugged left. She looked at her phone and then another guy walked in. I was like WTF? But I decided to give her some time to see if she hugs him too.<br><br>The guy sits down and after a few minutes, Wendy goes to him. She takes his order but I seen her kiss him on the cheek. I got up and left and she seen me. She left the bar and walked to me. She asked if I followed her to work and I said yes. I told her I saw her hug and kiss a guy and she said she knows the guy that she hugged. She said the guy that she kissed was actually an old boyfriend. She said the guy she hugged was a friend. I didn’t believe her and that’s when she slapped me across the face. I told her to stop because I was about to hit her back. She asked me why I was getting mad at her and I said it’s because she’s cheating. I said I saw her text messages. I said “Did you forget that you left your phone logged in?”. <br><br>She asked me why I’m getting mad at her over messages and I showed her the texts from the unknown numbers. I said I want you to tell me who they are. She said one of the messages was from her brother and the other was from the guy she hugged. She said her brother’s phone was out of order and she was texting him on his new number. So I asked her about the message from Sammy. So she said she didn’t know what I was talking about. I then explained that I was on her phone and I saw messages between her and Sammy. She said she doesn’t know anyone named Sammy. So I told her I took a screenshot and sent it to myself. She asked me to show her the messages. So I showed her the messages and she said it was a message from her friend Samantha. <br><br>I asked Samantha who? She said Samantha from high school. She said that Sammy was her nickname. She asked if I knew that Sammy was a short name for anything beginning with Sam. I said I don’t care about nicknames or anything. I want you to leave me alone. She said that I need to apologize to her for going through her phone. I laughed at her. She just turned and walked away from me. I followed her home and I locked myself in my room. On Sunday I seen her leave and then I went out to the living room. I turned on the tv and saw a message on the table. The message was "Leave. I don't want to see you again. - Wendy". <br><br>I grabbed my car keys and left. When I came back that night I seen her car was gone. So I opened the door and went in. I seen her bags were gone and I seen a note on the fridge. She wrote in the note "I'm going to get a lawyer and sue you. I will also be removing my name from the rental". I went back to my car and cried a bit. In the end I’m like AITA?