Brady, I'm going to be a little hard on you, my friend, because I suspect you want to listen to people's advice but your heart just isn't ready to commit to protecting yourself.
She is using you. She knows exactly how to handle you: through words and sex. You sound like someone who is very emotionally dependent on her.
It's not going to last. Whatever you want from this relationship isn't going to happen. Your girlfriend knows exactly where you stand and understand perfectly that you're so weak-willed and needy that she can get away with just about anything she does to you. She is abusing your character, and she doesn't care.
Her crying is mere corodile tears. She knows what will win you over. It doesn't mean a thing to her so long as she can string you along and keep you as a faithful backup plan. Once her "soulmate" comes into the picture, you will be nothing but gum beneath her shoe. Do you not understand why she doesn't care? Because it is just so easy for her to say jump and for you do so without hesitation.
She's sees herself as the one in power and loves it. She knows she could just snap her fingers and you'll give her the world.
She is abusing you and its important you understand that she might very well ruin you for life. You will have a very fucked up view of relationships. This will transfer to your children. You are fucking up your future because you're being a doormat.
The people here have been telling you to wake up. You can't because you're afraid.
Buddy, people will leech off you until there's nothing left.
In high school, I dated a girl for four years. She cheated those 3. I found out almost the same way you did. She was never remorseful. I made the mistake of thinking that something was wrong with me, that I needed her and she was the one. 2 Weeks later, I realised what a pathetic sac of beta I was. I grew a backbone and dumped her immediately the same day. She didn't care at first. But as soon as I found someone new, she became remorseful and jealous.
It was only 5 years ago that she sought me out and apologised for everything she put me through. Her relationships never lasted and I was the best thing that ever happened to her. She changed herself and was mending fences to the people she loved but wronged so much. I was strong and committed to my wellbeing back then. She commended me for my integrity.
You need to be this type of person. You need to be selfish and look out for yourself. You might need IC. I recommend it. You're too young to understand the harsh reality of real love. Real love isn't a fairytale filled with rainbows and unicorns. Its sweet but ugly. It requires great sacrifice. It requires suffering and learning. It requires people with strong morals and character on every end. Your girlfriend is not only cowardly but lacks morals that fit in your relationship.
She is going to cheat when you're married. It's going to happen because you will let it happen. In order for someone to learn from their mistakes there needs to be consequences for their actions. Through consequences, a sense of failure and loss, can someone learn more about themselves and about what they should see as right and wrong. Your girlfriend has no consequences for actions, so she'll do it again until something bad happens from it.
You will regret that you didn't act sooner. It's understandable to be on the rollercoaster, but you need to focus or years will fly by and you'll be left with nothing but thoughts of a different future where you left her and found someone beautiful and amazing. You'll have no one to blame but yourself.
Stop being a pathetic doormat, my friend. You deserve better than what she's giving you. If a cuckhold lifestyle is what you want, where you're just a backup financial plan and she screws every other dude on the side, then continue on. But if you want someone that will cherish you for the rest of your life, someone that will put you first every time, then dump this girl now.