He has a sexual addiction and is apparently in love with this other person but will not leave home. She continues in an uncommitted relationship with him but has other male friends also. The moment we separate she and he continue to engage in more open relationships. His sister and mother are now friends with her. She has made a permanent mark in my marriage of 15 years and we have 5 children. She is ten years younger with no real responsibility. She we seek counseling or should I leave and let her have him with all his issues?

I think you need to seek counseling not to keep the marriage together (I don't know if there is one left), but to be able to disolve what is there as amicably as possible. You want to try to keep the situation from affecting the children anymore than it has too.

You need to see a divorce lawyer as soon as possible to find out what your rights are and to begin the process of setting up child support and visitation.

Good luck in what ever you decide to do.

His family is now friends with this woman? Do they know what's going on? Where is the respect for you, his wife? I guess I am having a hard time with that. Why is he making this public and getting family involved? To me he sounds like he is over the marriage and wants to be with her. Have you spoke with him about any of this at all? Does he want to work on it?

There are too many questions here...

Why won't your husband leave home?
Why are your MIL and SIL friends with him?

And, more importantly, why have you put up with this situation for 7 years?

I think that it's far too late for counselling if it's been going on for 7 years and she's become a fixture in your marriage. Sounds as if he wants to have his cake and eat it too. It's time to grow a backbone, get good legal advice and leave him to his cheating GF.

I'm sure that life will be much less pleasant when he has to deal with the realities of life - it's time to look after yourself now, rather than supporting him in his menage-a-trois.

Gemini is right. You have allowed this to happen for so long that its almost a way of life in your marriage now. Either put a stop to it for good. Or walk away and be done with it. I personally don't see him giving her up after this long.