I was cleaning my Sig 250 and when I attempted to reassemble the slide would not go on. It felt like it was hitting something solid....all of a sudden the entire slide barrel and trigger assembly was in one hand, and the empty frame was in the other. I cannot separate the trigger assembly and the recoil spring is squeezed

The takedown lever wasn't in place. It's going to be easiest to work with if you put the fire control unit back into the grip module first. Place the back end in, slide down and aft, manipulate the trigger enough to get it through the cutout in the frame.

You should be able to work it back and forth until it unlatches and pulls free.

Lift the slide releases, depress the trigger and work the slide without pulling up.