Help me

Recently I found out my husband had feelings from an old relationship (she’s now my beat friend) and lied to me about it for two years and now I’ve been catching him lying to me about pointless stuff with her for no reason. She has his ring from school and I seen his message saying I want it back and I’ll give you the one I ordered but don’t send it through her because she don’t know you have it. Both her and him lied to me about not knowing where the ring is. How do I handle this since I’m not supposed to know and violated his privacy looking on his phone. This situation is getting to much to handle but I don’t know what to do