Summarising your problems:
- No oil shows on dipstick ever
- You keep adding oil to no avail
- Oil keeps coming out of unexpected / undesirable places
- Bike still runs
With the engine idling, unscrew dipstick and look in the oil tank: is oil being returned into the tank, use flashlight if necessary.
If you see oil flowing back into the tank, that's the indication that the return crcuit is functioning.
BTW: I'd be highy surprised if you don't see oil coming back. This would mean your tank empties itself and the oil feed pump would be starved of oil.
After your 15 minutes driving, stop the bike, not the engine, and while idling unscrew the dipstick, quickly after stopping. Observe oil level (eye, not dipstick). Let idle for a while and keep observing what happens to oil level. Let us know the results.
Question: do you know anything about the oil pump: was it replaced already, how many km's on the bike, etc.
The hose with the filter at the end, is it the one coming from the engine, just behing the cilinder, diameter approx. 12 mm?
If it is, this is the breather hose which is normally connected to the air filter.