Dear Mr. Sharma
After reading your problem it is very clear, as mentioned above by other participants also, that this relationship is not workable and you also know that. You helped a lady in need and both of you crossed the limits. At the time you entered into this scene, that lady was a victim being cheated by her husband and hence she was thinking of committing suicide, as told by you but know she must have come out of that trauma and knows her mistake/ fault also.
You need to talk and ask her about future course of action for both of you. I think she will not stop you from getting married but she may ask you to continue this relationship also. So, the first step is to mentally prepare her about your marriage. Once it is clearly understood between both of you next action can be decided.
You have to make a point about the future of her son. Here some other points which matter are the financial position of her family, your financial status, her educational qualification etc. Is she a working women? Does she holds any professional qualification? What is your qualification and status? Is she in a position to do job or some business? What is the present status of her relations with husband?
Further advice or discussion depends upon the reply to above queries. If you wish to discuss further pls give the above details.