My simple advice would be what a few others have echoed
NO bird is worth losing a mate over
What i have learnt is when it all goes shit with a bird, who's there to fall back on? Your Mates.
Its your mates that stick with you when it all goes tits up, and pull you through.
Its your mates who are there to take you on a good night out to clear your head when a bird has fucked you over.
Honestly mate, if this lad is a good mate, then no bird is worth it!
Birds come and go, but its your mates who are their for life.
My advice would be to just stay away from her, it wont be easy but its the only way. Seeing them will only make it harder for you. A few weeks in Magaluf will do the trick