Wow EnFpFer just said it all!
Fortunately I don't think everyone is doomed to this pattern IF they are reflective and open to other people and try to get out of it. Ergophobe, I know what you are talking about and I wish I knew of a good way to get people to see what they are doing to themselves!
I have seen a couple of women devote their whole lives to an impossible cause that is twisting and isolating them and their children in the process and often even ruining their health and other relationships. My sister is a prime example of this and yet after 20 years, I still do not know how to help her.
The key preventative elements are:
1) Don't get into a relationship before you have a solid sense of self and a support system in place of people whose lives you are contributing to and involved with and whom you can lean on as well.
2) Balance is crucial to maintain a healthy relationship. When any one thing/person in your world becomes the most important, perspective gets off kilter and it creates a lot of unhealthy pressure as well on all involved.
3) Self-care (whether health wise, reducing stress, getting into positive habits, making wise decisions about who to spend time with, not indulging addictive behaviours) sends strong cues to those nearby about how to value the person.
4) People need non-romantic opportunities to practice establishing expectations and boundaries that create healthy relationships.
5) People need a variety of perspectives in their life to help guide them. This is why balance between family, work, friends and relationship matters. It is also why they need different types of people and to voluntarily seek out others' advice or views so they are making informed choices. They need practice doing this before getting into a serious relationship where it is going to be even more difficult to ask for help when it is needed.
Once the (INFJ) person is in a relationship though, I think caring enough to risk conflict with the person is probably important, understanding that it may make all the difference, or it may make them very upset. Also, sharing your own experiences indirectly is useful. Often though, both are difficult because there is not enough proximity to be able to do so. The relationship where they are suffering emotional abuse is too important to them, and it also has isolated them. One possible way to help address that is to look at what needs are being satisfied through that relationship and seeing if there are other ways of offering fulfillment for those needs so that they do not have to hang on so tightly to something that is so destructive.
After 20 years with a very insecure and misathropic man, missing countless family gatherings and other events, my cousin did make some changes. She was 37, and decided that for the sake of her children she needed to start losing weight. The weight she lost, allowed her to realize how little time she ever took for herself and to deal with her family's resistance to her doing so for exercise. The confidence she found from seeing them come to value her more as a result of her valuing herself, as well as the the empowerment of seeing pounds coming off allowed her to start standing her ground in other areas as well. She still accepts more than I think I would, but has started realizing that she needs relationships, positivity, fun and emotional ties in her life. As a result, both her husband's and childrens' lives have been greatly enriched, even though she felt very selfish and guilty about it at first and encountered great resistance. The perspective she's gotten from having friends/family to bounce ideas off of has also allowed her to realize how out of whack things had gotten before without her ever realizing.
I find it harder to draw lines for people close to me when there is not one over the top event that is a deal breaker. Sometimes relationships ebb and flow - people are closer or more distant. It is hard to determine what is natural, what gradual small changes have added up to big unaccepatable ones and where one's own behaviour factors in to all of it. In this sense, I think we can greatly benefit by experience of other people, both in observation and conversation. Also keeping a wide enough range of people in our lives so that we have some checks and balances when our perspective otherwise could become skewed helps tremendously.