In such a situation you need to check the sentiments of that lady by informing her that your family is planning for your marriage. Watch out her expressions. If she over reacts you need to tell her that this relationship is not going to work long and in case you both r caught it will be much more embrassing situation.
Tell her that in the eyes of everyone her husband is guilty at present but in case your relationship is known to all you might not cope up with that situation.
Now, since much time has passed since she felt emotionally week and in present circumstances she must not behave the way she did earlier.
Tell her to keep herself occupied in some work and help her in finding some job or starting some business. Keeping her busy will help her in coming out of this situation.