Overheating - Did I kill my 91 Jeep Cherokee?

I've been driving from Iowa to Nevada since yesterday morning. It was going over the 210 temp guage line a little bit and I was worried as it would keep creeping up. I turned on the heater and drove about 1000 miles that way. (Its tough to do in 90 degree heat) I get to Utah and it goes up and won't stop. I pull over just as it gets to the red and shut her off. Coolant starts bubbling out from under the resevoir cap. I wait a while and put what water I have in and then try to drive a little further (stopped at a view area, wanted to get to town) and it overheats right away. I think that maybe I didn't give it enough time or enough water/coolant. My buddy who was following me takes me to the nearest town and I buy some coolant/water. We get back to my jeep about 45 minutes later and it takes 3/4 a gallon or so. I start her up and we watch it idle for a bit to see how its doing. About 5 minutes later the temp guage is red again and its leaking out under the cap. Did I break it for good? It has all my stuff in it as I was moving and I'm so broke that this is just a nightmare. I have it towed to a repair shop but they can't look at it until the morning. Could it just be a thermostat? Or was it a thermostat and it finally broke something else after driving it so hard? Did I crack the block? Or would this be other symptoms? I'm so nervous to hear from them in 8 hours I can't even think of sleep. Any help would be so awesome. Thanks.