You made two mistakes, IMHO. One you already identified yourself...splitting your empire. The second is not eliminating Pontus before taking on the Seleucids
Had I not made the first, the second wouldn't have happened. Had I attacked Nicomedia instead of Halicarnassus (still don't know what I was thinking), Seleucia would not have attacked me because my army would not have been where it was. That said, I learned a valuable lesson about what HA's can do to pure infantry armies. Greece has attacked. I promptly kicked their tails. I will train my HA's as garrison in Halicarnassus, then go north to Nicomedia. I posted that Pontus besieged Sardis, it was Sinope. Sardis is rioting because I was unable to afford to upgrade. That should change soon, I first had to upgrade Sinope to a large city, which took more money.

Then the Lord awaked as one out of sleep, and like a mighty man that shouteth by reason of wine. And he smote his enemies in the hinder parts: he put them to a perpetual reproach. Psalm 78:65,66 KJV