Its something that I will never know. Unless I ask that guy directly.
He may obscure the truth and lie as well. Or deny everything. He may belittle your manhood and laugh at you. Or not speak with you at all.
Or even worse:
He may tell you every graphic detail of his sexing your woman. Things she did with him that she'd never do with you. Once you hear any of those details, it will be forever burned into your brain. It will haunt you, taunt you, torture you.
Now, ask yourself, do you really NEED to know this information? Move on.
Listen very closely to what I tell you: the reason you're stuck is because you're emotionally attached to this woman. The relationship has been broken, it's actually over, and so this becomes your only connection with her, like a rope, which is difficult for you to let go of because once you do, she's out of your life forever, and right now, that's too emotionally painful for you to bear, so you're avoiding cutting that rope.
But she's like poison to you. She's like a sinking ship that's taking you down with her. You've been losing sleep, experiencing loss of appetite. She's on your mind from the moment you wake up to appearing in your dreams. That's because this event has traumatized you, and the more you obsess on it, the deeper the trauma you'll experience. The more contact you have with her, the longer and more difficult it will be to heal. You need to save YOURSELF and get away from her sinking vortex and swim to the safety of the shore.
You are like the drowning person who struggles with his rescuers and has to be rendered unconscious in order to be saved. You are fearing life without her. But remember, you used to live life just fine without her. You can do this. You have to do this, for your own benefit, for your health, for your mental sense of well-being, and to be free.
You need to switch focus to YOURSELF now, and not her. You need to take care of YOURSELF. There is not ONE WOMAN on earth worth your health and sense of well-being.
You mistakenly think that because her infidelity is the cause of your pain, that having her back will purge the pain you're feeling. But that's a mistake in your thinking. The truth is, having her back is inviting back the person who will hurt you. Thus, having her back again would mean a life of hurt. And she will, odds are, cheat again and again.
Everytime her cell phone rings, everytime she's a little late coming back from the store or from work, or has to work late, everytime she has a funny look on her face, everytime she says she's going out with her girlfriend, every time she says something that conflicts with what she said last month - you're going to wonder if anything's going on. You'll feel you need to check on her emails and facebook and cell phone records, and that's no way to live. That's not the wonderful relationship you want for your life.
This battle is fought in your mind. You have to put her out of your thoughts, not dwell on her. You have to cut off contact COMPLETELY. Do not call her, do not answer or return her calls. Just take care of business and get her out.
You have to fill your life now with your hobbies, find new interests, explore old ones, delve into your passions, play sports. Hit the gym regularly, get a new haircut, change your life for the better. New doors will open. Keeping busy will help keep your mind off her, and it will minimize the importance she held in your life by making large every thing that's more important. This is YOUR life. Don't waste it pining for someone who doesn't want you.