Only you can answer this question. It could have been anyone.
My advice would be to ask for a sign of who helped your fiance in the same way you originally asked for help, and then try to be open to any strange coincidences and research all the demons on the Joy of Satan to look for a connection to said coincidences.
For example if you start seeing a specific number over and over, then look what demons might be associated with that number. This is one of many possible examples.
Signs can also be quite blatant, such as seeing a sigil during meditation, or randomly seeing that demon's name in a place you'd never expect.
Everyone's experiences with the Gods are different and personal so I can only give hypothetical examples of what you may experience based on my own experiences, and this is why it's important to stay open and do research once you've reached out