When should I add ING after "to"? What if I don't add ING and just leave the verb in infinitive?
*You and Daniel can always return to being friends. *You and Daniel can always return to be friends.
*I want us to go back to being friends. *I want us to go back to be friends.
*The secret to learning prepositions *The secret to learn prepositions
"To" in those sentences is a preposition, and prepositions are followed by nouns. Gerunds (-ING forms) are nouns, which is why they're used in those sentences after the preposition.
"Go" and "return" are usually followed by "to", because we go/return somewhere. It's a preposition describing movement towards a place. That place isn't always physical, just as in your sentences. "Being friends" is an emotional place with someone.
"Secret" is usually followed by a preposition to talk about the kind of secret it is. Usually this preposition is "to" or "of".
That's a good question, Johnny. Your examples all require the gerund. The mini-article that I wrote on the subject two months ago turned out to be extemely popular, so you'll definitely want to take a good look:
I think there isn't much of a rule. However for these sentences we would always use the -ing form.
In my mind, the logic is the friendship is a continuous state you want to "return" to. To use the infinitive you could say: "you could be friends again". It is the return/go back that is preventing you from using the infinitive.
Learning prepositions, you would need to use "how to learn prepositions" - however, here the meaning has changed slightly. How to learn prepositions, once you learn something it is a completed act. Learning prepositions is a continuous act.
Like I said, there are not many rules around this problem, English is just messy sometimes!
For more info check here: