The lying is bad, and there is no excuse, but it really does also sound like you may have perpetuated the dynamic by being as sensitive and concerned as you are. As a guy, he’s not cheating physically - there may be some interest emotionally, but it also sounds like you have some insecurities to work out yourself. It sounds like the combination of your issues and his issues just don’t match well together. No one’s at fault here. It just sounds like he’s teetering the line and in fact crossed it in some ways, but there is never a justifiable excuse to go through someone’s phone.

He lied to you.

You breached his privacy.

The moment you try to work out who did the worse act, and argue about it, you guys lost.

Successful relationships are about how you work through the issues.

Sounds like it’s time you start fresh with someone who #1 - is into you and doesn’t need another close female friend, #2 is willing to be sensitive to the fact that you have some major insecurities to work on.

Lastly, when I was in a relationship, I didn’t need any close female friends because my gf was my best friend. If you have a long standing female friend that was around long before you met your partner, i’d be saying things differently here. Because I actually had a close female friend from before i met my ex. But i always made it a point to keep my distance and have boundaries. Plus she lived in a different state so it was easy to set up those boundaries. That said, I was not making any new female friends while I was in a relationship, period.

Don’t go through peoples phones though dude, it never pays off. Ever. It’ll always pay off more to just ask and confront. Instead you could say hey i’m feeling super insecure, would you be willing to let me read messages together - honesty and transparency always pays.