Same sex Marriage : Indian guy & spanish boyfreind living in Germany

I am indian guy and have spanish boyfriend. We both are planning to get marry soon. He is spaniard working in Frankfurt and soon I will accompany him there as i am moving to germany for my 6 month language course.

We both are planing to get married there in germany when I am doing my german language program. Being an gay do I need to proof that I am single (certificate of marriageability) because in India we don't have any authority proving this. Secondlly homosexulity is illegal here so I will not gonna get any certificate of marrying my boyfriend.

We want to get marry at Spanish consulate in Frankfurt; is that possible to do..? Can we register our marriage in Consulate and then apply for residence permit in germany using our registered marriage document...?

What document I may need to get establish to get married in consulate ..

Please help...

looking forward to hearing you guys soon..!