What can I do for my nephew?

My nephew (21) is Gay and has only come out to me and my 18 yo daughter. He is very adamant that he does not want my sister (his mom) to know because she is very religious and strict. My sister goes above and beyond for him, always has and I know she will accept him if he told her. Nonetheless it is his decision to come out to her and I respect that. My issue comes with me seeing him be so isolated. His dad hasn’t been in the picture for a very long time. He doesn’t have friends he hangs out with other than his younger brother and my son. He has had a plan to una live himself and I did go to my sister with that and he got counseling but he did not tell the counselor or my sister the truth. I would like to take him and my daughter to a gay function/club. I really don’t know where to take him but my hope is that he will see other openly gay men be themselves in a public environment. I want him to see that he can lead a very open life and accept himself and love himself. I know I am risking my sister getting upset but I feel that this is so important. I know it’s not completely right withholding this from my sister but would it be completely wrong for me to do this? I don’t like seeing him turn into a hermit and stay in his room all the time. I want him to go out with his peers and him know that it’s ok to live his life.