Social media relationship trust issues

Hey every,

Thought i would share something thats really been hard for me to process lately. My partner has been a little strange with her phone, like i asked to simply borrow it to use the calculator and she wouldnt allow it, and tried to say she was using it, i brushed this off but about 2 weeks ago i decided to open up her phone whilst she was asleep (i know this is wrong) but i wanted reassurance my worries were all in my head, i found she had been snapchatting her coworker and had a snap streak of 170, which i thought is quite a while for me not to notice her snapchatting this guy. When i askd her about it she said hes just a friend and really supportive to talk to about her work problems, she said i havent been there for her the past year or so for the emotional support, its true, i got very comfertable in the relationship and would almost get home from work everyday and sit on the playstation for hours at a time. And if she would tell me her work stresses i would sort of just say oh ok and not give her much in return. I asked her if she could delete him off snapchat as i dont feel comfortable knowing what snapchat is known for, and why cant she just talk to him at work. She got upset and has since logged out of snapchat alltogether and hasnt been on. She says she loves me and doesnt want to hurt me so she would rather just not use snapchat but she keeps telling me little lies and keeps information from me saying its because she doesnt want 1 million questions if she goes somewhere and a guy from work is there, for example a few days after the initial snapchat blow up, she said she was going out for tea with girls from work, everything was fine but later i logged into her snapchat and checked the snaps from the guy from her work that had built up since she hadnt been on, there was one that he sent to her sitting directly opposite her out that night for dinner when it was suppose to be “just girls from work”. i know it wasnt just him and her but i dont know why she keeps this stuff from me, is there more going on? Or does she ligitimatly not tell me so i dont question her Or get upset? She knows i have her snapchat login so why would she get upto mischief??

I wanted to post my own unique scenario to try and get some insight, as reading similar things on the internet its hard to get a full understanding.

what is everyones thoughts? Should i be worried?

thanks.