Hello @Serenata and welcome to our community :)
If you want to get married in Turkey I would suggest that you get in contact with the Turkish authorities and ask them which documents you need to provide or if there are other things you need to keep in mind. I don't know if you need to get in contact with UNHCR. Maybe @Marcel or @Steven know more about that.
It is possible for refugees with a residence permit to travel to Schengen countries if they got their residence title in a Schengen country (for further information see these threads: https://www.wefugees.de/k/questions/1653
). BUT: Turkey is neither a member of the EU nor did they sign the Schengen agreement. Therefore Sam will probably need a visa to travel to Europe.
Broadly speaking a refugee looses his status if he travels back to the country where he came from or if he is planning an act to threaten public safety (e.g. terrorism). Traveling is not a reason to loose the refugee status. But again: You probably need to get in contact with Turkish and Dutch authorities to check how they handle cases like that.
I hope this answer is helpful to you. Let's see if the community can provide further and more detailled information.
Best regards, Thorgen