Is it ok to talk to sister-in-law about marriage problems?

My husband and I deeply love each other but there is an issue on his end that, no matter how much I communicate with him about it, shows no signs of stopping. My husband has a twin sister and I've considered coming to her with the problem and asking for her advice. Is this ok? I've made it clear to him many times how I feel and nothing changes, but no one knows him like his twin sister. I just want help, sometimes an outsider's perspective will help things.