been there, and crumbly texture is definitely fixable.
When you get a crumbly, dry looking Gouda, it usually comes down to time and heat control in the beginning.
Did you cook the curds too long, or at a temp that was a few degrees too high? Over cooking squeezes out too much moisture and makes the curds brittle. also did you spend too much time overall from adding the culture to pressing? The longer the process takes, the more acid develops.
For your next batch, try to shave 10-15 minutes off your total make time, and monitor your cooking temperature very closely