A girl named Gabby revealed that she had moved from the US to England for a relationship, only to find out that he was cheating on her. But she found out in an interesting way. Someone told her to check her Blocked list on IG. She found a girl that she didn't know and didn't block but after doing some investigating she realized her man was cheating on her with this girl!
I would have never thought of this. But since the girl was blocked Gabby wouldn't see anything the girl was doing on IG, like liking her mans photos or leaving comments and vice versa.
So I hope you don't find anything but keep this tip in your back pocket.