Girlfriend is looking at phone (her Instagram page). She's happy and in a stable relationship.
Couple go on holiday - happy montages but suspicion starts to creep in
Boyfriend starts coming home late, dodging calls from girlfriend, Girlfriend wakes up - he's not there next to her etc. She internet searches for a private detective. Phone call to arrange him to follow the boyfriend to find out why he's acting weird.
Detective follows the boyfriend, taking photos of him at a jewellery store, having coffee with woman etc.
Girlfriend is waiting for Boyfriend to come home (sitting at table with photos on hand). She has his bags packed ready to kick him out for cheating. Confrontation. He leaves (montage of scenes from earlier but fully explained)
Cyclical structure - Girlfriend is looking at phone (her Instagram page). This time the girlfriend is crying as he's left her.