F-1 Sponsor: father of girlfriend ok?

[severineledoux]

Greetings. My boyfriend of 5 years and I have gotten into US schools and now have to apply for I-20 forms and then, F-1 visas. My father will be paying for both our education, our apartment and our expenses. So we're both going to state my father as the sole sponsor and he will provide the letter and everything. He's my Dad, so no questions here, but I wonder — will the sponsorship letter be enough in my boyfriend's case as "proof of relationship"? Or should we look to further prove our relationship — and Dad's interest in boyfriend's life, i.e. by bringing in photographs of us together over the years? Thank you all very much in advance.