Verification Against EU Law

hello, everyone

My partner (EU citizen) and I (non-eu) are not married but in a committed relationship and want to apply V.A.EU.L. How we met is we were volunteering in an organization in the NEtherlands through an Erasmus+ program. Soon after we met we entered a relationship together and basically moved in togethersoon after that within the organization, we were living together from March till December. After that i had to go back to my country because my volunteering visa ended. They ended up coming to my country and we rented an apartment together for 3 months, but we cannot prove this because there was no official contract or municipality registration. Now i came to the netherlands with a tourist visa and we are hoping to apply. My question is how can we prove that we have lived together without an official renting contract? Would a personal statement from the director of the organization be sufficient proof that even though we were living in a big house with more roommates, we had a room as a couple?