Loneliness is a big deal here, particularly if one or more of these factors describe your situation (others may have more factors to consider than I):
1. Not working
2. Susceptibility to alcohol
3. Married
4. Accustomed to privacy
5. Extraverted
6. Intraverted
7. Comfort food, weight control
8. General cultural, legal and personality anomalies
#1: For me, working is a must in a long-term situation. I always separate my social network members from my professional networks. This is critical everywhere including home.
#2: German beer is amazing. Liquor selection is limited. Don't bother asking for a Martini, I've not met any bar tender who knows what it is. You can train bar tenders, and a sense of humor is always nice so as not to belittle anyone, for example they will ask which glass, because germans are raised with a concept of this is correct, and this isn't, which is problematic, because it stifles innovation, but I digress. Tell him no, no, not that one and point to an ashtray and smile this one. But seriously, alcoholism is really prevalent. Particularly here, not because of culture, not because of amazing beer, but reasons I stay clear of, so I won't give opinion, but be careful. There are differences in culture that matter, however, covered in other sections below (I doubt I'll have the room to finish this dissertation... sorry...
#3: Men and women out in public are considered to be rude if they have eye contact let alone smiling or stopping to chat. Especially if you have a wedding band. So to me, it's rude and presumptuous to feel that way. I'm not unfaithful, you're not all that, and it's all about what's correct and what's not, so again social progress is stifled. I miss seeing an attractive person and catching a smile. That's not any obligation to even stop to chat. It's just human. But not here.
4: Auslanders will be interrogated by some, but it's not an unfriendly discussion, albeit somewhat masked by curiosity, but living here you realize it runs deep -- do not take it personally -- you'll be frustrated and for no reason. I'm not being racist; why do I mention it then? Because here, if I don't, then I leave myself wide open to be assumed as one, which is the opposite from the general assumption in the USA (please don't zack me for generalizing; it is not pointing fingers; it's a two way street). All I'm saying is, there's notion that in Europe (not generalizing about Germany), the extreme left has destroyed everything and so some may view you as part of the problem. Obviously, avoid talking politics, but you'll find that many germans don't avoid it at all-- interestingly USA politics. They're experts in ways that after 4 years in Germany, I wouldn't dream of pretending to know about German politics. Please be aware that some will be expert conspiracy theorists. Just let it go. Just nod and say "interesting, listen I have to go, I'm sorry " because that's no less superficial and actually more constructive. Lastly, german speaks with more potential to spray or blow air at you. For me, I have a personal space that seems normal, like maybe 24 inches away. Here, that may not be enough, and, depth perception gets worse and worse with alcohol to the point where I almost step off a barstool and they almost fall off because they lean into you -- American people do the same thing, but even st a table without being drunk, if you are paranoid about germs, go ahead and cover your beer because nobody even notices it. It's not insulting them. You know why? I think for a very cool reason-- they're looking you in the eye. It's not mean. Don't overreact. Nobody's meaning any insulting behavior. Lastly, what may sound like perfect German to you isn't necessarily coming from a german. In other words, don't assume something coming from a fluent speaker means it's a native german. In all fairness, though the USA is also multicultural, we have Canada, Mexico the Pacific and Atlantic, while Germany borders other countries which border other countries. You drive 8 hours in the states you're in a different state. Here, you're in a different country.
#5&6: Both are listed because there's pros and cons. I think you should be aware of perception that you are responsible for, such as being really extraverted towards a few people, but not all people. Seems normal for americans, but here, Germany has a really friendly protocol. Do not clink a glass without looking each one in the eye. Don't drink to something. Drink to someone. Don't get weirded out if they get touchy-feely. Don't make any public jokes. Joking is everywhere in USA bars, unheard of here, and, at someone's expense is not funny here either. Especially here. Don't talk about others.
#7: Spicy foods (here, sehr sehr scharff means a little extra pepper). You can train restaurants to do it your way, but I believe being grateful and tipping is important in any country, but I tend to stand alone in this view despite the clear fact it works for me.
#8: legally, it is critical to understand that laws here are not the epitome of justice. Meaning justice is, like the USA, handled in court. But the laws are based on control. It's really easy to get into trouble because some you g people, doesn't matter if they're German or not, can hide behind these laws knowing you can be dragged away even though you were I the right. Don't get all big and bad here. Don't be tricked into aggression. You'll pay dearly. Don't flip off a driver -- no witnesses necessary, it's 3k euros fine, with no more than 30 days to pay it.
All of these things may not seem relevant to loneliness in Germany, but if you're staying here long term, especially if it's not because you wanted to (I love Germany and German people, but my contracts are why I'm here).
If you don't want this posted, no problem I'm probably not going to be describing the norm for 90 percent of expats, but it's been a long haul. Being American is not bad nor great here. It's being kind and respectful; if you have that, then being American makes you rare, because though I love our troops, there's no doubt they've left a trace of disrespect for Germany -- doesn't matter if that's true or not, that's a perception.