What foreign language should I learn and how?

I don’t know which language you should learn, but I thought I’d share a method: I recently found out that I have access to Rosetta Stone for free through my public library. I was just on the library website and started seeing things I hadn’t seen before, so kept exploring, and then there it was! I don’t know how widespread that is, but it’s definitely a program Rosetta Stone offers, so your public library might have it, too?

I also don’t really know how it works (Rosetta Stone’s website says their “Library Solution” offers 50 hours of foundational instruction, so it might just be the first level of their program, but that’s still something, especially to get started!)

I would suggest learning Italian because of your boyfriend’s connections. If you ever visit Italy it will be useful. Italian citizenship entitles you to live in many EU countries but not the UK due to the Brexit vote. Learning a foreign language is a big undertaking in time and effort and I would think hard before taking it on. If you decide to go ahead the mylanguageexchange website can put you in touch with a native speaker.
PS I’m not sure that link is working but you can find the website easily by googling.

Russian or Chinese, depending.

Duolingo and Babbel are two free online language courses. You can sign in and spend a short amount of time daily. Of course, there are upgraded features you can pay for but the free is fairly good. Also, fairly basic. I tried it for French but I was too advanced for the early lessons.

For what you want, I would think Italian would make sense. Even if you don’t move there, it would be fun to vacation there and try to use it.

English is spoken in most Western European countries. Italy not as much as Germany and the Nordic countries, but still you can get by fairly easily in Western Europe with English and minimal knowledge of the local language. I only mention this, because if you go to live in Europe, you can get up to speed once you land there and not have too much difficulty while learning the local language.

My experience is that most Europeans don’t speak much Spanish, except for the Spanish of course. Italian and Spanish are similar languages, so if you learn one it will help you with the other.

I lean towards Spanish, because if you never leave the US it will be very useful. Or, consider what language is most useful for your career.

Chinese is useful as the Chinese gain economic power, but are you likely to live in China? The Chinese also have their new generation all learning English in school, so again, Americans luck out with English being our primary language.

If you move to Italy can you get working papers immediately as a spouse?

If you move to Canada only the province of Quebec is French speaking, and in Montreal there are plenty of people who only speak English and minimal French. If you work with the public in QB you need to be bilingual, but otherwise not so much. French is a second language for many people in Europe and so is German.

Spanish. There is a program on PBS called ’“DESTINOS:” an introduction to Spanish.’ Attend a college or community night course on the language.

Casual way to learn a new language effectively. I read an article about this guy who did just that. Need time to recall who he is and will post the link as soon as.

I’d go with Italian, for the reasons you mention, and from there the other Romance languages should come fairly easily, if you want to go on.
Considering where you live, you probably have the option of taking a conversational anything class nearby, which would expose you to more variation of inflection and pronunciation, and maybe supplement with a commercial program.

The best way to learn a language is to practice 15 to 20 minutes a day every day. Language apps are helpful but, as I understand it, they don’t give rules. You are supposed to pick them up on your own. It would be helpful to accompany an app with a standard language textbook to provide things like verb conjugation rules and lists of exceptions. The exceptions are important to know, since they tend to be for the most common words.