http://prntscr.com/o2gytz my Headphones are on default and in OBS i have it also on default.
That might be your problem. If your headphones are your default output, and OBS is set to send its monitoring output to the default, then it will echo.
If you're going to use the Monitor feature to listen, your monitor device cannot be the default device, or OBS will record its own monitor output.
Either set default and monitor to be separate devices, or turn off monitoring on the devices that are echoing in Edit > Advanced Audio Properties.
Windows often changes the default output device during startup, and this will affect OBS setup. So it's possible to not touch something and for nothing to change for a long time, and then one day, the default devices have altered. This is why I usually suggest disabling all devices in Settings > Audio and add devices directly to Scenes as audio sources, and copy them to scenes as required rather than depending on an audio sources set in Settings > Audio to be present in all scenes.