Help me please,what happened?

i have to male betta fishes in a 10 gallon tank witha seperator in it. 1 of my bettas are fine but the other one just floats at the bottom of the tamk near the seperator and goes to the top 4 air and then goes back down and lays there.I also noticed that he was swimming around in circles when i left 4 fishing thi morning and when i came home a few hours later he stoped.so i fed him and whent out side i just came in about a half an hour ago nothing happened but just now i looked in his tank and i saw that he made a medium size whole in the middle of his gravel what is wrong can some one tell me help please!Is it a enfection why did he put that big whole in the gravel help me please!!!!!!