Just about all of us have had this experience. That's why we are here. Sorry to hear about your situation.
The decision to end it is totally yours to make. Everyone has their threshold. My only advice would be not to make decisions based on emotions. It's devastating to find this information out and your initial reaction is play book text, we've all reacted the same.
If your going to throw in the towel, take some time to process what has happened and approach it from a rational mind vs emotional hart. Detach from her and her actions and take some time to reflect on what you want and what makes you happy. After all, what's the rush? As you said, you have been at this for 2+ years so what will a little more time hurt? She doesn't know now what life would be like without you, why don't you give her some time to find that out before making a decision?
"It is curious that physical courage should be so common in the world and moral courage so rare." -Mark Twain
