Don' know what to think about relationship?

[whatever]

Awhile ago, I saw my girlfriend using this social media site, so I decided to make an account and message her, but didn't tell her it was me as a surprise. Instead I got the surprise when she started flirting and saying she was single and asked to skype.By then I told her it was me and I got upset, but she apologized, and I made it seem ok. Her excuse was that they gave her attention that I didn't give her which is bs because she told me otherwise not even a month earlier. Later I learned that somehow she made the whole thing my fault to her cousin and friends, which didn't seem right to me. Then, awhile later, she said one of her highschool guy friends stopped by randomly for a chat. I read through her texts, as we do to each other for laughs sometimes, I found that they had planned to meet up for an hour. She started all these excuses that didn't make sense to me. Should I be worried? Ever since the first thing I have trouble trusting her, even though we've talked about it.