girlfriend 21F keeps texting other guys including ex situationship 20M?

I started talking to 21F about 5 months ago recently things have gotten serious and I notice everytime we’re together she seemingly hides a bit of her phone specifically of other guys she texts after seeing a few of an old relationship I drew a line for it after a few weeks she kept doing it I told her to unadd his number and put the hammer down and she did. Before we started dating we had a brief one week period where we didn’t talk to each other much because of a small argument ( this has nothing to do with anything and all is good now ) and she started talking to a new guy who she never has been friends with it now has been 2 months and I consistently see she talks to him quite a bit this guy also doesn’t know she has a bf to my knowledge of what she’s told me. Most texts with him are just normal talk but it’s quite a bit. I’m not sure if I’m controlling to tell her I’m not comfortable with this as I already was upset with the ex relationship. Any advice helps