Well, I think the movie nor the short story give enough information to reach to that conclusion, at least to me. Maybe Ennis did have some friends, but they were married and didn't have enough time to hang out with him when he divorced. Besides, Ennis was seldom around. When he wasn't working at some far away ranch, he was with Jack at the mountains where nobody could see him.
Also, considering that he didn't want anyone to found out about his secret life, is undestandable that he woud avoid making close friends. But that be out of fear, not necessarily homophobia. Cassie was the closest friend he made after his divorce, and she had a hard time understanding Ennis. She didn't know where she stood in his life and has to ask his daughter about it.
On the other hand, Ennis talks about Don Wroe letting him use his house. He has to be someone Ennis knows pretty well. I mean you don't let a house just like that, you let it to people you know and trust. So I guess this Don Wroe person was someone who as a friend of Ennis. Cassie also talks about some guy named Steve. When she runs into Ennis at the bar, she tells him she has left a message for him with Steve at the ranch. But he could be his boss or whatever.