i may have crossed some blackwires on a switch
You likely switched wires.  It sounds like the thee wire pairs consist of:


Power feed
Line to kitchen light switch
Line to basement light.  


From your description switch was being used to bridge the power feed to the kitchen light using push in connection and the screw connection.  (This may not be to code.)

It appears the power feed and basement light are on the same side of the switch.  Try moving the wire on the screw to the other screw.  If this fixes things, the power feed is on the screw.