He is only leaving for a short time.
Auxiliary verb+ only (Adverb)
There are only blue ones.
I only wanted to tell that.
Only often goes with Nouns. Note the difference:
Only human beings think. (No other creature can think.)
Human beings can only think. (That is all human beings can do)
In writing, you can try your best to put ONLY juxtaposed to the item emphasized. This is done to make the emphasis as clear as possible so as to avoid being misunderstood.
Only Bill saw the anaconda. (No one but Bill saw)
Bill only saw the anaconda. (He only saw and leave it sleeping)
Bill only saw the anaconda. (Bill only saw the anaconda and left the zoo)