I would agree with what Rose76 said your daughter is 29 she is very capable of making her own decisions and with that being said should fully understand the consequences she may face if she stays involved with this unfaithful man. I'm sure it must be hard for you to have to sit the sidelines and watch your daughter go through this but she must go through it only knowing that you as her mother are there for support and support alone. Question: Does your daughter come to you seeking answers/help and advice? It sounds to me like she does and maybe she needs to understand that her problems as an adult are not your problems. I would start by letting her know that you are always there but only to listen and explain that while you wish there was more you could do the decisions are hers to make. I wish I could be more helpful but I am no parent and in my past experiences I am just like your daughter even our ages are the same. I too would go to my mom seeking help with relationship troubles because we are close like best friends but I could see the stress it put on her and well these days I try not to confide in her so much on relationships anyway and when she asks me how things are going I just say it's ok and then change the subject. I hope this helps