When to tell the friend the truth?

My best friend is in a relationship with a huge d-bag. My husband and I met him once on a double date at a pool hall. My husband talked to him and I talked to him and he came across as a guy that was really just interested in a good time and not a long term relationship. I have let it go for a long time that I can't stand the guy. She will email, text, call me with how he's acting and how she thinks he's cheating on her with her friend. And I have told her on more than one occasion that this is what she can expect from him. So get used to it or move on. Today she compared my reactions to my husband, who I have been with for years, to her boyfriends reaction to her.

My husband has self pity issues. Coddling him doesn't help, it only makes the matters worse. So I have realized that I have to jump his butt to get him in gear. We have actually been on the verge of divorce for the way he handled stress before (he would drink and he can't handle his alcohol). I don't do alcohol or any illegal substance and have moved out because of the drinking that stemmed from his inability to handle the stress in the first place.

Another man talked to her on facebook and her "boyfriend" has now broken up with her because of it. Her comparison of her boyfriend and me really broke the camel's back. I opened my trap and let it fly! I finally told her how I really felt about her boyfriend. Was I wrong? I don't know. I have sugar coated everything up until now. I have been tactful when she would contact me and complain and what a jerk the guy is. All she ever says is she just loves him so much blah blah blah. So today...she got the total truth. :explode: Maybe she will be my friend tomorrow...

When do you tell your friend the truth about anything?? Whether it's if their significant other is cheating, they are d-bags or whatever.