I'm looking for information. How does it work that after you meet a woman on the site, visit her, and decide you want to be together that you end up together? Is there a different visa application for significant others?
I can't say about other countries, but for the USA, if you marry overseas, then you file a petition for an immigrant relative (I-130) and not the fiancee visa since the spouse is legally connected to you when they enter this country. The USCIS website has the form that can be downloaded. Also, an affidavit of support needs to be also filed (I-864). If you are sponsoring a fiancee, form I-129F is used. For other countries, I would look for their website information.
I believe the fiancee visa has a shorter processing timeframe because it is issuing a 90 day temporary visit to the foreigner. If you should marry her here in this country, you would then need to file for a green card application for her shortly after the 90 day period. For the fiancee visa, you do need to submit proof that you met the lady and are not some kind of human trafficker. I believe you also have to be financially responsible for the lady during her time here. As for the immigrant relative visa petition, there is more documentation involved with filing. You need to include translated forms if you married overseas (that incluses marriage certificate, health immunization records, children birth certificates (if any), a form from your local secretary of state office affirming that you are a single and can marry immediately, A US State Department form affirming your marital status and citizenship, an affidavit of support form that includes salary information and financial asset information. Some of rhe forms are required before the foreign marriage (for the foreign country officials) while others are needed after you return back to this country (to the USCIS).
In either case, you have to show that you two physically were together. If you are married overseas, you do not have to apply for a marriage certificate in your home country. The married overseas foreign spouse application will take longer because it requires more processing time at USCIS here.
One thing that I forgot to mention. Neither the fiancee visa nor the immigrant relative visa is a "sure thing". So if you get rejected for some reason, your marriage will turn out to be a "long distance relationship". On the fiancee visa side, there is no direct impact to you since you did not marry the lady.
One very common reason for rejection is insufficient financial assets/salary. The US immigration laws do not want "legal deadbeats" to flood this country. Note that the "illegal deadbeats" are in this country already.