You have a good chance that a head gasket will fix it. You could have a bent rod or whatever, but if it was sucking coolant while running, it may very well have been throwing it as fast as it was coming in.

If it were me, I would pull the head and check for a bent rod with focus on that cylinder. If there is no bent rod, I would do a valve job while the head is off and put it back together.

You are probably going to get it back in good shape with the the head work.

Best of luck,