I'm dating someone that has a very close friend of the same sex that is clearly hitting on them. I gave in & snooped and feel horrible about it but they were sending my s/o hearts & stuff. I felt sick at it & myself & quickly exited their phone. I brought it up that I'm not comfortable with the friend thats hitting on them & wanted to seriously discuss it & they just shrugged like "oh well" and changed subjects. They've lied about the friend in the past and idk anymore.
You clearly don’t trust your partner, and maybe you have good reason not to trust them, because they’ve lied to you in the past about their friend, and they don’t seem willing to listen to your concerns. You could try talking to them about this again and asking them to listen to you. But if they don’t seem to care that this bothers you, and don’t want to talk to you about how you feel, then it doesn’t sound like any of this is going to change. If they don’t listen to you, you’re going to have to decide whether you’re happy staying in this relationship they way it is, or whether you’d be happier if you ended this.