Japanese language question?

こよう=来よう is indeed a volitional form of 来る/ kuru. Volitional form of any verb + と思う means "I plan to (do something)".

(Example: 来年留学しようと思います。= I plan to study abroad next year.)

So your sentence should be translated like this: I was planning to come (here)/go (there) leaving (something) at the hotel.

What that person wanted to leave at the hotel and where they were planning to go should be clear from sentences before this one, I guess.

The whole sentence translates to "I was thinking I would come to the hotel and throw it/this away"or "I was thinking of coming to the hotel and throwing it/this away"

Koyou is a form of kuru (I think it's the volitional form). The koyou makes up the "come" in the above translation.

Any verb ending in -te (like sutete) + koyou + to omotte ita = "I was thinking I would come and [verb]" or "I was thinking of coming and [verb]"

Just extra info:

Without the -te verb at the beginning, simply

koyou + to omotte ita =

"I was thinking of coming."

Just "koyou," however, would grammatically not make sense, because when you use "come," it means one person is at the location in which they are inviting the other person to, but "let's come" implies that neither of them are at the location they want to arrive to even though an invitation is present, which is impossible. Sorry if this is confusing, I just thought I would clarify since "let's come" might make sense in English.

The appropriate "let's" phrase for inviting someone would be "ikou," "let's go" in English. (sorry again if you already knew this, your Japanese seems to be advanced)

Hope this helps! If you have any questions or if this was confusing I'd love to help.

Also the volitional form of suteru is suteyou, not suterou (^^)