FALL

Everyone knows how to express the idea of you starting to love someone: 

▪️ TO FALL IN LOVE WITH somebody

But if you know the good side, you have to know how to express something opposite, when you stop loving (not "stop to love"!) someone. The English language is full of irregularities, but here it's very logical, even conlangish.

▪️ TO FALL OUT OF LOVE WITH someone

Note "out of", it's these 2 particles that are opposite to "in", not just "fall out love".

And here we come to another interesting phrasal verb

▪️ TO FALL OUT

It has several meanings (as usually) but the most popular is "to stop being friends (lovers, etc)". And you must know possible continuations and prepositions used there. 

So when you need to mention that somebody who you're no more friends with, you say

▪️ TO FALL OUT WITH somebody, as in "Astrid fell out with some of her colleagues and decided to look for a new job."

OK, but what if you need to introduce a reason, cause of Astrid's falling out with her colleagues? Your phrasal verb grows bigger then and looks this way:

▪️ TO FALL OUT WITH somebody OVER something, as in "Astrid fell out with her colleagues over a stupid little issue, and now she's looking for a new job." 

If you don't know about OVER here, you might be trying to figure the way out using something like "She fell out with her colleagues because of a stupid issue". You would be understood, but now you know about the strongest option for this situation.

But what's the opposite of this "falling out with someone over something"? It's not "to fall in with somebody", among some options I could come up with this one:

▪️ TO GET ALONG (AGAIN), as in "The chief of staff gathered Astrid and her colleagues together and after a serious talk he got them to get along again."

But if what you're talking about is a romantic relationship being restored, you have this expression:

▪️ TO GET BACK TOGETHER, as in "Julia was hoping that her divorced parents would eventually get back together."