Thank you for reaching out to us with your question and I'm very sorry to hear about your situation!
What you describe doesn't sound lawful to me and a lot like discrimination against you by your neighbor and the house owner. Depending on your contract, smoking for example may be prohibited in your flat and it is not unusual for neighbors to complain about noise. But simply living in your home with your boyfriend and talking (even loudly) in your apartment are your right as the tenant. Unfortunately, there seem to be a lot of prejudiced people in Germany, who try to drive away people by telling stories to the house owner instead of talking to you directly (if they felt disturbed, for example).
In Germany, we have something called the "Allgemeines Gleichbehandlungsgesetz" AGG. I will try to translate it, as explained here: https://www.antidiskriminierungsstelle.de/SharedDocs/Downloads/DE/publikationen/Leitfaeden/Leitfaden_Wohnungsmarkt.pdf?__blob=publicationFile&v=1
The law forbids discrimination in the process of getting access to the supply of goods and services. Included is space for living (Wohnraum). The AGG protection against discrimination (Diskriminierungsschutz) includes six reasons for discrimination: age, disability, ethnic background, gender, religion and sexual identity. According to that, racist discrimination in the housing market is forbidden by law. This applies not only to the process of finding housing, but also whilst renting living space. If you find your rights as a tenant violated, you have the right to demand the discrimination to be ceased, even to the payment of compensation for the violation of your "personality rights" (Persönlichkeitsrechtsverletzung).
There are a few exceptions that apply. For example, it is lawful in Germany to ensure "socially stable inhabitant structures, balanced settlement structures and economic, social and cultural conditions" within renting living spaces (§19 Abs. 3 AGG).
Unfortunately, this paragraph often allows for (racist) discrimination to be overlooked.
What I would advise you to do is to collect proof of your situation. If you are in Munich, you can reach out to the "Mieterhilfe München", who help with questions around renting, problems and conflicts (also with neighbors). Here are their contact details: http://www.muenchen.de/dienstleistungsfinder/muenchen/1082659/
I couldn't come up with contact information for a specific anti-discrimination department, but they may know more details. Otherwise, there is always the option to contact the Federal Anti-Discrimination Agency, usually in bigger cases: http://www.antidiskriminierungsstelle.de/EN/Home/home_node.html
Hopefully, this information helps and you find support to solve the conflict in your house. Feel free to reach out to us again if you need any further assistance!
All the best,