I would definitely not approve, but as a friend, I would try very hard to only give advice when asked. However, I definitely have objections. I just can't see this situation turning out good for anyone. I have tried to imagine their lives as laid out in the novel and as much as I try, I just can't envision anyone coming out unscathed. My gut feeling is that Jane will end up hurt the most. Ultimately, she has the most to lose as she is the "mistress" and, history has proven the "other woman" usually ends up alone in the love triangle. As a friend, I can only imagine how hard it would be for me to physically be around this arrangement. However, as a good friend (to either of them), I definitely would feel an obligation to remain true to the friendship.