Stop being so weak and pathetic and start being more assertive towards this hooligan puppy.
Dominant natured adolescent pups will soon take advantage of a lenient and weak owner.
Its not hard to teach a puppy like this some manners.
If something unpleasant happens to him every time he tries to hump then he will soon learn not to do it.
At the moment this pup has no respect for you whatsoever.
carry a squirt bottle full of water and squirt him in the face every time he even thinks about humping and with a thunderous voice tell him "Off" or "leave".
Or....carry a can filled with pebbles and throw it at his feet when he tries to hump,plus the verbal "Off" or "leave".
It may take a few or more times before he gets the message and thinks twice about humping but he should stop eventually if you are persistent and do this EVERY time he trues it on.
Get him castrated as soon as he reaches 12-14 months old.