I feel embarrassed asking for advice

I feel embarrassed asking for advice but here I am. So I've recently been in a relationship with my partner of about 4 months we live together and she's an introvert Ie goes to work then comes home. We met by chance not via social media of any dating sites which is really nice. However my partner likes to communicate with male co workers via social media quite often somtimes infront of me which really helped me as my last relationship really damaged any chance of building trust with someone again. However one guy who frequently she would message via messenger I became suspicious due to the constant messages it happened most days id come home from work and her phone would go off and she would say something like ohh I wonder who that could be and of course it was this particular guy. After a few weeks I tried to have a calm conversation regarding this guy and asked who he was and how well they knew each other and she told me i had nothing to worry about she's knows him from her freind ship circle and he's a manager at another branch she works for she's only met him twice via work so with that response i said if you don't really know him that well then is there really a need to talk to him everyday ? She said I have nothing to worry about and I can trust her she even said that me getting funny about the situation reminded me off her ex and she got emotional which made me feel really bad. So a few more weeks have passed and of course the messages continued and I finally put my foot down and asked what was going on between you two I said to her if I was to read the conversations would I find anything I wouldn't like she's said probably and starting crying she ammited that before i met her that she and this guy where taking sexually via txt but insisted they had never met in person the worst part is this guy is in a long term relationship and my parenter said she knew that when she and him where sexting eachother which makes me think I cannot trust or believe anything she says. I packed all my stuff and said I couldn't trust her and I wanted to leave and she begged me to stay and she said I could read there conversations she insisted she hasn't cheated so I read the conversations between them there was some Minor flirting and some things that he said to her which really didn't sit well with me he sent a giff what said your my girl or something or another and she didn't even question him why he would say that another thing she said multiple times to him was I'm loyal with a 😉 emoji which implies she's not. She has since told me she will not talk to him as much enless it's work related because they have to communicate to an extent for work purposes. The he worst part is she is due to be transferred to the branch where this guy will become her manager. Another thing to add is about 2 months after being with her she had this 2 week thing where she did alot of over time and of course when she did this overtime she wouldn't contact me until it was over but in her normal working hours she had no issues replying to my txts. The thing is when we are together everything is great we are happy but after this I really don't know how to feel I'm just looking for an outside perspective on the whole thing.