https://mlpforums.com/topic/178267-s08e15-the-end-in-friend/
Here's a bit of "spoilers" :
The title is just for the younger audience, we know that they will remain friends.
Heck, when you think of it, this may the "Rollercoaster of Friendship" Of FIM S8
And we also know, that they'll find something to do together or help each other be more tomboysih (Rainbow helping Rarity) or feminity (Rarity helping Rainbow).
But come on, we know that writing staff wouldn't break off the friendship of two of the Mane 7.
So again the ending is predictable (story may be really good overall) , however we have to remember the title is for the younger audience watching.
Because at the end of the day, the creative staff has to be reminded, that is a show for kids (and to sell toys)