I agree with the comments above about a lot of these being financial scams. This article from Wired is interesting -- kind of a horror story of a worst case scenario of someone who got way too caught up in the fantasy: https://www.wired.com/2015/10/online-dating-made-woman-pawn-global-crime-plot/

I also read recently that organized crime is starting to get involved in these scams. I get a lot of them on Facebook and on another site. The men are typically age-appropriate and good looking (in their fake pictures), and usually say they are widows and doctors, fire fighters, or oil rig workers. Sometimes they're holding puppies, lol. It's best to just block and report them.