Why has my Iguana been more aggressive since i separated it from the other Iguana?

I had them together for about 3 months till one started getting aggressive so i decided to get a new tank the one that started acting territorial is now aggressive toward me i try to take it out more often and get it used to being handled and it seems to stress it so i feel bad and put it in its tank where it tends to seem sad almost i don't understand if it was the splitting them up or if its breeding season PLEASE HELP