I’ve been playing dnd for 4 years now and mainly DMing. Recently one of my players (my friend) quit our campaign because they didnt like it. Today, one of my players came to me about a campaign they wanted to co-dm with me to learn how to dm sayin that they didnt want me to help and they want another player (also never DMed) to be the other dm. I dont mean to sound controlling of my group but since this group came to be i have been the DM, others have tried their own one shots but i am the only one with experience. 

My mind is going to a place of feeling not good enough for my group and im now going into a burn out. Any advice?

so far it's just talk, right? everyone's still attending your game night? next time everyone meets for your campaign maybe end that night on a cliffhanger for something new: a genie offers the party one wish in return for helping fulfill someone else's wish, under the thieves guild they just cleared out they find an enticing teleportation circle beside a sign saying "bank vault (they'll never know!)", about to release a 'waterfall' of slimes onto a dragon's horde to carry away coins, just found an airship / spelljammer, etc... and end it a little early to ask if everyone's still on board to continue the story.

you might get an honest yes/no but even just shrugs and blank stares would tell you what you need to know. if the excitement has left this campaign, then it might be time to let it rest a while. either you'll come back to it later with great new ideas or else more things were wrong than you knew (in which case this is your chance to pause it on good terms rather than watch the friend group explode).

Or maybe they just want to DM and experience it.  I know I was a player, and always was thinking of various campaigns and ideas, then one day the DM said does anyone want to fill in because he was going to be busy and could not plan.  I said yes.  He plays and I DM.  We both are having fun.  It is not like they do not want you around.  And also, as you play see how they handle different scenarios than you.  

Reach out to your friend who quit, and just talk to him about what he did not like.  Something I always try to do is let the players have fun.  So i bend somethings sometimes.  Just bend, not break.  Work with him and try and come to an agreement.  And sometimes, a person just may have other personal worries, and just use the game as an excuse to leave.  Good luck.

Talk to your players about this; talk to them outside of gameplay, individually if possible. Tell them what you told us. Listen to what they tell you in response. Then talk to the whole group together if necessary. Figure out what changes, if any, need to happen. Make those changes.

A player becoming a DM  is the natural progression and as for the one player wanting the other to be co-dm   maybe they were spitballing  and their individual ideas feed the others  allowing them to create something that might be good.  Being asked to take break and be a player is not a bad thing.

My single greatest pride as a DM with decades of experience is helping people go from being a player to also being a DM!

We can't run all the games, just ours. Definitely seek feedback, but also be open to seeing this as a sign of your success. You've shown them enough of the game and enabled them to express their stories.

Run a short published module. See how they respond. I don’t know, what you are describing sounds toxic. It’s not good…players out of the blue saying  they want to co-dm? Why? Or even how? Do they have a clue as to how to setup a map or an encounter? Who knows..all group dynamics are different. But this sounds sour.

I wish I could be a player again. It's been years.

I play and DM, prefer to play so when someone else shows interest in DMing I offer any help I can. If they are asking you for help, they may resent you if you don't. I am not saying your wrong for feeling the way you do, but baby birds are gonna want to fly at some point you can fight it or help them, your choice. 

Quote from Agile_DM >>

My single greatest pride as a DM with decades of experience is helping people go from being a player to also being a DM!

We can't run all the games, just ours. Definitely seek feedback, but also be open to seeing this as a sign of your success. You've shown them enough of the game and enabled them to express their stories.

 This is or should be the goal of any dm. To help the players to become a dm. 

In all of my campaigns I've asked that if my players want to run a game or one shot they can. 

Many have and all of them are now a DM. It's the greatest wonderful feeling. 

When players want to run a game, let them. They only do it because they have a great dm and players at their side. That's us as the dm.