While it's possible to apply for a marriage visa based on a short-term visit, there may be additional requirements or challenges in demonstrating your intent to establish a permanent life together in Cambodia. Generally, the purpose of a marriage visa is to allow a foreign spouse to join their partner in the country of residence for the long term, and a visit of only one week may not be sufficient to establish this intent.
Some additional factors that may be considered include the nature and duration of your relationship, your future plans, and whether you meet any other eligibility criteria for the marriage visa. It's important to carefully review the requirements and provide thorough documentation to support your application, including evidence of your relationship, such as photos, correspondence, and any legal documents that support your intention to marry and live together in Cambodia.
It's also worth noting that the processing time for marriage visas can vary and can sometimes take several months or longer. Therefore, it's important to start the process well in advance of your desired date of travel, taking into account the potential timeline for your fiance's visit, the visa application process, and any potential delays or complications that may arise.
For the most accurate and detailed guidance, I recommend reaching out directly to the US Embassy in Cambodia or seeking advice from an immigration attorney who specializes in Cambodian visa matters. They will be able to assess your specific situation and provide personalized guidance on the best approach for obtaining a marriage visa under these circumstances.