What could have cause my clown loaches death?

I had 1 clown loach in a 36 gallon tank with 4 black phantom tetras, 4 mollies, and 3 glofish. I know some think clown loaches are aggressive but they actually are not. He was a peaceful fish. They fake dead a lot but his eyes were dialated and when I took him he didn't flap. What could have caused this? Did he need a mate like all the other chaps? Cuz everyone else had a mate.