My friend is a great guy. He's been dating this lady for over 3years and some months now, and they have had their fair share of ups and downs, misunderstandings and disagreement. But Everytime they disagree, they'd always settle and life goes on. Their love for each other seem to be only true in books in cartoons.
Sometime this year, he proposed to her and engaged her with a ring, with the view that he was gonna do formal introduction to her family by MAY, but for the fear of Covid 19 and the lockdown, he had to just wait.
Now, the issue is, there's this guy in his babe's life who seems to be a threat to their bliss. His babe is so fond of this guy, she doesn't pick this guy's call in the presence of her fiance but she picks other calls. Infact, my Friend told me that he went through her chats with this other guy sometime around April last year when she came home from school for a 2 week break, and what he read almost left him paralyzed.
His babe has been going out with this guy, and collecting gifts and money from this guy in question. My friend confronted his GF but she kept being defensive of the guy and she told my friend that she and the guy were just friends and nothing more.

Just last week, the lady came around for one of her cousin's wedding and my friend went through her phone again. This time, he discovered that she was already deep into this relationship with this other guy.
My friend confronted her and typical of her, she defended this guy so we'll, you'd think my Friend was an enemy.
Mind you, that other guy is still a student and this my friend is done with school, working and doing well for himself.
Now... He's in a dilemma and doesn't know if he should just end the relationship, as this his girlfriend is bent on not breaking ties with the other guy...
Please advise .