Jealous 😤

Okay so, my boyfriend just came back  from a month trip overseas with the school. I'm overseas for another 3 weeks so I don't see him for a while. Now the photos have come up on Facebook and one girl has posted many with just him, as they have become really close on the trip, and she has a rep of being very flirty. As I'm looking through these photos I'm trying to not get super jealous but I can't help it. Like I miss him so much and it makes it a lot harder seeing him having the time of his life with other girls. How can I stop being like this and get over the pointless jealousy??