A couple is looking for a flat for 3 years, students in Germany

I would like to tell you a little about me. I graduated from St Petersburg Polytechnic Uni in Russia this year. I am 21 years old, in October I will be 22. I work in an online English school, but my mother will pay for the apartment, because my income is not so big, so my mother is going to pay for the flat. Also I will open a bank account, where it will be 11,000 euros according to the rules of the University. I like travelling. I have been working since I was 18 years old and, as I wrote earlier, my salary is not so big, but I can afford to travel twice a year.
I would like to lube in a flat with my boyfriend, we have been together for 7 years, so it's really important for me and for him. He is also a student in Germany.