Mrs Toast speaks much truth, as do a great many others. For myself, had I a partner I lived with, then inspecting each others phones for text, messages or mail would be verboten. Any shared devices, like pads or whatever, would be set up so that either emails were disabled, or we had several accounts that were public/private. I wouldn’t dream of checking someone else’s mail or text, the very idea makes me squirm uncomfortably, but I have known very close friends with partners who do such things, and it never has a happy ending. Such people are inherently controlling to an unhealthy degree, and generally almost impossible to wean off that behaviour, they just can’t help themselves.
Greedo, I’d have passcodes on my phone, were I you, and just say ‘goose, gander’ when confronted about it.
But that’s me; anything for a quiet life, but there are limits to what I will tolerate.