Can a girl leave me after 6 years of dedicated relationship ?

I have been with a girl for long 6 years she came from a lower middle class family now when she is established she is leaving me with no reason. We have consulted a psychiatrist for a counselling during the counselling she told the reason of her breakup after 6 year are some basic issues of relationship which orchid 5 years back. We were in happy physical and mental life I don't know what happened she is leaving me now. With no reason. Most probably as she was established right now she doesn't need me. She promised me of getting married in 2019 which I postponed due to her career in 2020 she brought family in my home they fixed our registry date and she broke up next. I don't want to see this relationship in like this. if she once breakup without understanding my feelings I want to see the end of this relationship. So seeking legal advice. She is not involved with any other person in in any other relationship she is saying me that I will not try to fix it. Han family is menu plating hard which may be the problem of this matter I am just guessing this. What should I do to take a legal action against this ?