Friendship Advice

I don’t know if this is a good group to post this in but I just feel helpless, my best friend is going through a bit of a rough patch with her husband that has cheated multiple times. He is so toxic and feel bad for even saying that.. I could never say that exactly to her I try to tell her how I feel honestly because she’s my best friend but she has decided to forgive him and work on their marriage, which I do support... But I don’t support her being used and walked all over & repeatedly cheated on. I just hate it. How can I be a supportive friend? I just want her to be happy! 😭