Military boy/girlfriend needs you to pay for leave? #ItsAScam
99% of military profiles on dating and social media sites are fake ones, being used by scammers for romance scams.
If you are in contact with someone claiming to be a member of the armed forces who says that they need you to request and pay for leave for them, then it is a scam. Members of the armed forces do not have to pay for leave, it is earned by time worked, just like any other employee earns their leave. There is no need for them to pay for their leave, transport back from leave or whatever other excuse a scammer uses to try and get you send money to them.
The military also do not communicate with random strangers on the Internet about serving personnel, which is what you are - you aren't the soldier's husband or wife - how can you be? You've never even met them in person, let alone undertaken a marriage ceremony.