Peeking at my girlfriend's cell phone message and finding that I'm still having an affair with my ex-boyfriend, what should I do ~

You can reconsider your place in her heart. If you still love her, be generous. It is not a glorious thing for a boy to peek at his girlfriend's text message, even if love is selfish. It's no big deal to keep in touch with your ex-boyfriend. I also keep in touch with my ex-boyfriend, but only as friends. If I'm ambiguous, I'm probably just saying. Boys should not be too stingy, especially not so stingy as to peek at their girlfriends' things. They should respect each other. You just have to apologize, show your attitude, and then let her choose. Nostalgia is human nature. As long as you care about her enough and take care of her enough, most people will still choose their current boyfriends.