On the positive side, GL has a really interesting and colorful setting, and did a good job of bringing in (/allowing) really interesting and colorful characters. Unfortunately, solid writing and solid DM'ing are really very separate skills. I know firsthand that it's really easy to get so wrapped up in one of those that you don't even notice yourself fucking up the other one, so I definitely don't blame you.
If you'll take my recommendations for the future and in general, I'd say that an important thing is that DMPC's are inherently dangerous and should always be used with extreme caution. If you have to have a DMPC, try to avoid making it a powerful DMPC - players that end up in conflict with it will resent the unfair matchup, and players working with the DMPC will get to feel gypped about how it's always effortlessly stealing their spotlight. Players generally only like DMPC's that guide their actions by means of occasional helpful tips, ideas, and exposition, if they try to guide their actions at all, and play a generally supportive role to the party.
If you have to have a powerful DMPC, try to minimize outright conflict with the player characters. Once they just stop wanting to listen to the DMPC altogether, you're down to either forcing them to play along with the story you want, or changing its direction to account for how the players are no longer inclined to be cooperative with an asshole DMPC.
And finally, if you have to have a DMPC, and it has to be both powerful and abrasive, then... well, make sure it's also expendable.
Anyway, like I said, not really blaming you. It was an easy mistake to make, which, due to the nature of the beast, unfortunately ended up backfiring disproportionately hard. I've killed my own fair share of RP's with incompetent GM'ing before, so I know how it is. Still, it's worth not giving up on. Just remember where it took a bad turn, and move on. Eventually you get to where you suddenly realize that you've been doing a pretty good job lately, and that's a satisfying realization to have. Pretty worth it.