I think Gu Manlu was in love with Zhang Yujin, but if she hadn't been so cold to him, she would have never made the mistake of letting his sister go.
I think Gu Manlu loves Zhang Yujin, if not for the fact that Zhang Yujin was too cold to her later on, and transferred her feelings to her sister, maybe Manlu wouldn't have done it, and let her husband rape her sister like that.
Previously, when I watched "Half Life", I felt that Gu Manlu was a horrible woman, and if it wasn't for her, Gu Manzhen wouldn't have ended up in such a pitiful state. Later, as I slowly got older, I slowly started to understand Gu Manlu as a person. In fact, she was nothing more than a poor woman.
If it wasn't for her broken family, she would have had no choice but to become a dancer, and she would have been able to be with her first love, Zhang Yuzhuang. But the actual situation is that she went to be a dancer, in that society, no matter she is physically, or spiritually are not worthy of others. She chose Zhu Hongcai is a last resort, if there is a choice, she certainly will not choose him. If she had a choice, she definitely would not have chosen him. In one place, some women went out to be prostitutes when they were young, and then went back to find an honest and poor man to marry. So why do these women look for an honest man? Because many honest men are not well off and do not know how to sweet-talk, so they cannot get married and have to make do with what they have. But these women are not settling, if they have a good job, coupled with their beauty, surely they can find better conditions.
After Gu Manlu married Zhu Hongcai, his business was getting bigger and bigger, but he was not good to her at all, he laughed at her and satirized her. For Gu Manlu, she was tormented in this marriage. In her memory, her memories of herself and her first love were still good. Perhaps she still imagined if her first love didn't get married because he was waiting for her. When she learned that her first love had moved on to her sister, her spirit ran wild.
So Gu Manlu still loved Zhang Yuzhuan, it was because she cared too much that she went crazy and acted irrationally.