“It was meant to be” comes pretty close. But then you could also say “it was destiny”.
I don’t think destiny is a good fit because destiny implies there is no choice. 緣分 is something that can be cultivated like karma, and there are more different kinds of 緣分 than just romantic ones.
I don’t agree with this premise. If you put destiny or fate in the past tense, you are in the here and now. “Us being together now, was our destiny.” “It was fate that we found each other.” And I think that is exactly the concept of 緣分. 我們在一起是緣分. It’s not about what keeps us together in the here and now, but what brought us together in the past. Am I missing something?
Oh, after doing a bit of reading l realize that the meaning of 緣分 is actually quite different from fate and destiny. It just seems to be used in similar circumstances.
Turns out the 緣分 is more about people having a deep bond or connection between each other. Interesting 
That’s a great description. What you do with being brought together from deeds of the past is entirely up to you.
Density.
Does it really matter? As mentioned by @ninman, close enough is close enough. I think people use the English word “destiny” to describe what you’re asking about, at least in some circumstances.
I’ve had this sort of conversation several times with Chinese speakers, trying to convey the idea that there’s sometimes no 1:1 semantic mapping available to you, so you just go with whatever delivers an approximation. It usually ends with “your English is really bad”.
- The proverbial saying “have fate without destiny” (有緣無分) refers to couples who were fated to come together, but not destined to stay together, and as such is sometimes used as a break-up line.
Does “happenstance” work?
Serendipity?