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The easiest way to divorce is when both spouses agree. In your case (since your wife does not agree on the divorce) you need to prove that the marriage has definitely failed, which means that there is no chance for it to be saved.
The usual procedure is that you have to live seperated from each other for one year. If your wife still disagrees after that year, you have to provide evidence that your marriage has failed. That could be that she is expecting a baby by someone else or something like that.
If that's not possible you have to live seperately for 3 years. After this time-period you can hand in the divorce petition at family court ("Familiengericht") on your own.
You wrote about some serious tension between you two. This could build the ground for a special case where you can file a case of hardship ("Härtefall"). If a court decides that it is unacceptable for you to be married to your wife any longer then the deadlines stated above do not apply anymore.
Source (German language): http://www.focus.de/finanzen/experten/trennung-der-ehepartner-muss-der-scheidung-nicht-zustimmen_id_6244663.html
Concerning your interview: Unfortunately it's not unusual that BAMF takes some time to decide on your case. Broadly speaking you can file a so called "Untätigkeitsklage" at Verwaltungsgericht after 6 months. But since you need to consult a lawyer for that (which will be quite expensive) it's usually the only option to just wait.