Pilot reported that during cruise the door latch came loose resulting in the emergency exit door opening in flight and eventually detaching from the aircraft. Pilot diverted and made a successful landing.

Narrative

I was at 15;000 ft flying when I noticed my door latch was starting to come loose. There are 3 parts to the door latch. The hooks; (which are inside the aircraft and hook onto the door to keep it shut) the handle; and the knob. In order to move the handle out of the locked position you need to push in on the knob and pull the handle at the same time. On Date however as I was cruising at 15;000 feet I noticed the knob was starting to rotate a bit and the screw on the knob looked loose; then it went in as if it was pushed. At the point the handle fell back because the knob was no longer keeping it in the locked position. Causing the hooks to unhook from the door; which subsequently led to the emergency exit door opening in flight; I held onto the door for 2-3 minutes trying to keep it under control. I slowed the aircraft down as much as I could to help. But the door then ripped off the hinges and most likely landed in a field. At that point I requested priority and turned direct to ZZZ and made a normal landing there.