My girlfriend is married but we have been together for 3yrs. She has told me that she is getting divorced but she never goes through with it, she blows it off. Why does she do that knowing that it hurts me?

Just the fact that you are asking total strangers why a person does what they do indicates to me that communication is not your strong suit.
You say NOTHING about her, not even if she has kids with him, or if they own a house together, or what you being 'together' actually means, or how well you get along, a thousand little details that are clues.
Find a quiet time tonight to sit down for a heart to heart, but instead of giving her the third degree, explain YOURSELF and how you FEEL.

You ask the wrong question my friend. You should be asking why you keep going back for more hurt?

SImple answer here...

She's using you for some fun on the side.

She's not leaving her husband... its obvious he offers her more than you do... even even if you did... you would soon find yourself being the one in the same situation her husband is in now. How could you ever trust her.....how could she ever really trust you?

She's married, and you know it. No sympathy for either of you with what happens now or down the road.

Hi! You're a booty call. A affair. She has no intention of leaving her husband for you. You need to end this affair and move on.

What it sounds like is that your "GirlFriend" is comfortable in the life style that her husband, not you, is giving her and wants to keep that stability. She is USING you for whatever she does with you. I wouldn't stick around, you can find a better person. Some food for thought. If she leaves her husband for you, how long until she gets another "BoyFriend" like she did with her husband?

All responses except mine are from men.
My first thought is that the hubby is supporting her, either alimony or child support. But hey, that's my female POV.

Look at her for what she is... a cheat and a liar, she's no good for you,you need to walk away if you don't you are equally as bad because you know she cheating on another bloke... or one day it will be you.

You're honestly surprised that a woman that has been cheating on her husband, the person she made a vow to, a legal commitment to, has been lying to you for the three years she's been cheating with you?

Seriously?

I'd be more shocked if she didn't lie, since lying seems to be what she's good at.

Your GIRLFRIEND?? Lets see. You buy her things, take her out, have a good sex life BUT-she will stay where she is and use you again if you let her.