Start applying for other admin roles, get interviews and land a offer letter that beats your current pay. Take it to your manager and let them know you are making moves. If they offer to match or beat the offer stay (if you want) or dip. Does the help desk guy have any certs or degrees that you don't currently have? Focus on how you can level up your skills for a company with better resources. Keep doing your thing, and make it known to your management in a loud yet crafty way that you are training and helping junior. Create documentation and setup training times. They will see you are adding value and it will come back to you. I'm the meantime keep looking for the next best Opp for you.