1. No offence or even a civil wrong has been done by her.

2. Law does not punish a man/woman for cheating on his/her partner. Even Section 497 IPC which criminalised adultery has now been struck down as unconstitutional by the Supreme Court.

You cannot file any complaint or case against your ex in this situation it's better for you to move om with your life. 

See merely sending a notice will not help as such there is no locus so sending notice is futile.

Don’t file any police complaint against your ex girl friend 

litigation is long drawn and expensive proposition 

If you issue legal notice she would file counter case against  you of stalking 

What relief would you claim in the notice? There has to be some cause of action in your favour, to send a notice to her, none exists in your favour.

1. Are you getting treated medically for your depression? In that case, you can sue her for compensation and medical costs. You would have to establish that your medical condition is due to her ditching you. 
2. It's not an easy case. You should not appoint any donkey advocate but an expierenced counsel to plead your suit in court. I'm prepared to handle this, but I need an exhaustive consultation session with you first. I'm based in Mumbai/navi Mumbai and as you are habituated to travel to Thane, it should not be difficult for you to visit me for exhaustive consultation.

Dear Sir,

If you are from India, You can file a case on her under section 415 of IPC.

If you have the evidence, submit them to the concerned Police Station where the case is filed. If the girl is found guilty of Cheating, then the court will only be able to order with imprisonment of either description for a term which may extend to one year, or with fine, or with both. There is no guarantee of you getting a compensation for the ordeal.

Do also keep in mind Section 415 of the IPC is a criminal offence, so this will be a criminal case against her.

415. Cheating.— When a person, fraudulently or dishonestly induces another person to do something which he would not do otherwise, and such an act causes or is likely to cause damage or harm to that person in body, mind, reputation or property.

You or law cannot force a women to continue relationship with a guy. She is free with her orientation to hook up with any one and how many. If you push her, she might file molestation/rape/blackmail etc charges against you.

So better control your emotional break down, its common and have another gf. Ek ladki ka dukh dusri dur kar degi.

You cannot file any complaint against your ex girlfriend on the basis of the the facts narrated by you.

Complaint can only be maintainable if she had exploited you financially.

Sending the legal notice would also be of no use. 

As a grown up adults both of you have your own liberty and till the date you are not married and is in consensual relationship you can not force each other.

But if there is any cheating related to money that may only be taken up 

- Supreme court declared that , when  a man and a woman in love live together , is part of the right to life and not a criminal offence, and further live-in relationships is legal in India.

- Hence, only due to the reason that you was in relationship with her ,not give any cause of action legally ,to file a case against her . 

- But , If she has taken monetary benefits from you on the pretext of marriage, then that may enable you to file a complaint against her for cheating.

- However, since you are in depression and facing mental harassment due to her cruel acts  , hence you should send her a legal notice after mentioning that , due her cruel behavior etc and breach of trust of relationship, you are facing trouble , and thereby inform her for apologize ,otherwise you will be forced to file a Defamation suit against her. 

Good luck and dont forget to rating Positively.

You can file a case of breach of promise to marry. But proving the same is very difficult in the court. 

Hi

Yes you can go ahead with a legal notice for atleast letting her know that she have not done good.

And listen brother.......

Life is very very long.....

Live happily 

You will get what is yours .. whatever the situation be.

and what is not yours you will never get it.

So move ahead and look forward to a happy life. 

Thanks 

I am sorry but you can't. The girl can but the law presumes that your consent does not matter. 

You could send a notice to her through an advocate and he can state that you have suicidal tendencies becasue of hwr betrayal and hence she should compensate for the same.

Regards 

There is no law which will enable you to file any

complaint or case against her, on the ground that s

chose somebody else over you for marriage.

Don't issue legal notice, she can file many cases against you .

No complaint is maintainable.

You have admitted that you cannot force her to marry you.

You have admitted that she is maintaining relationship with someone simultaneously.

You have admitted that she has cheated you.

Then what's the reason that you want to pursue the matter.

No complaint for cheating is maintainable.

She has not extorted any money from you.

She has broke the relationship due to the dispute between you both.

Hence just ignore her and look for your other works now on

No use of sending any notice because it may backfire with defamation case also.

Better forget this as a bad dream about move on in your life.

1. No you cannot make complaint against her for breaking up with you or having another relationship when she was in relation with you. 

2. It can bring more trouble for you instead of her. 

3. It will be better if you let her be and move on in your life.