When to stop?

[Ruby]

Yes, what they said.

You've got to listen to your head and your heart. Ask yourself, what are you getting out of this relationship?

If the relationship were to continue as it is, five years from now, what state of mind and body would you be in?

Relationships may need to end for a variety of reasons:
You aren't emotionally satisfied,
the relationship is harming you mentally or physically,
you are giving far more than you are getting,
you don't feel safe,
you don't feel loved,
your partner lies to you,
you don't trust your partner,
you aren't being treated the way you want/need
... and the list goes on.

IMO: If you are being abused, whether in a d/s or not d/s relationship, it's time to end it.

Here's a link to a great quiz. Are you being abused, doubting yourself or not sure? This one helps by letting you qualify degrees of never, rarely, sometimes and frequently.
http://www.aardvarc.org/dv/abusequiz.shtml

Here's an article and checklist from a BDSM point of view:
The Difference between BDSM and Abuse
http://www.sscn.org/abuse.html

In the USA, that National Domestic Violence Hotline Website provides excellent resources whether you are the support person or just wanting to validate your situation.

http://www.ndvh.org/educate/abuse_quiz.html contains a quiz similar to the one above that can help.

Note: Safety Alert from their website

Computer use can be monitored and is impossible to completely clear. If you are afraid your internet and/or computer usage might be monitored, please use a safer computer, call your local hotline, and/or call the National Domestic Violence Hotline.
1-800-799-SAFE (7233)
1-800-787-3224 (TTY)

All the best to you.