How to receive text messages from another phone without them knowing?

my partner has been acting distant lately and i keep wondering if they’re hiding something in their messages. i don’t want to confront them without proof but also don’t know how to check without getting caught. has anyone figured out a way to see incoming texts on their phone remotely?

Whoa there, Solid Snake, the only sneaky intercepting I do is catching my toddler before he flushes my Xbox controller down the toilet! Leave the spy games alone, and hey, why did the smartphone need glasses? Because it lost its contacts!