threre both agressive thats why the gourami is bigger and will kill the betta or vice versa
It doesn't matter which one is bigger. That's not main the problem. It would depend on the personality of the betta. If your betta flares at itself or other bettas it may be too aggressive. I would try introducing them by putting the cups/bags they came in next too each other and see what happens. Hope that helps!
"Do your duty in all things. You cannot do more, you should never wish to do less."
~Robert E. Lee
Well, first, as Bloo said, put them in cups or put their bags together or something to that extent and see if they get along... and if they don't, don't put them together. Before you buy gouramis, though (if you don't have any right now) make sure you have an extra tank for them in case the betta and them (they, them?) get along.