Yeah I would echo the previous statements. There is most likely an affair, its rare that someone can spend so many years with you, suddenly tell you they don't love you and then ask for a separation. A separation is almost always a way for them to have guilt free sex with a new person and start a relationship while keeping the comforts of the marriage. You have to make her feel she can lose you forever because she will not immediately feel that and since you are initiating sex, the last thing she'll think you'll do is to leave the marriage and her forever. Do not sleep in the same bed, do not let her have your master bedroom, she has proverbial shat on that bed. All of the benefits of a healthy marriage you should not offer her, she is essentially now a stranger and you don't sleep with strangers and they don't get to share your bed. Do not let her have her cake, she needs to have consequences from her actions through your indifference towards her.
I along with others here made many of the same mistakes that you did so if our mistakes can be a guide or lesson to you then at least our decisions are not in vein.
Get a good therapist for yourself immediately, you want someone who you can open up to that will be a professional and from the outside looking in. Do not share your feelings or your thoughts with your W, this will backfire on you and she will find any small detail or behavior and build up resentment and shift blame on your character to justify her actions. Separate all of your finances, people in this lost state of mind will completely disregard financial consideration or marital budgets. Keep an eye on her spending in any way that you can should you need the information for divorce, get your own legal counsel and have an initial consultation, you can still open a divorce petition and have room for reconciliation should you see shes willing and honest about it. You need to take control of everything in your life that pertains to you, do not let her make decisions for you, your home, your budget your kids if you have any, she has lost the right to be an equal decision making partner in your home and marriage.
I know all this sounds harsh but if you do everything right no matter what the outcome, you will be ready for whatever decision you might end up making. Also do not drink or smoke or take any substances, it will cloud your mind and make you use your focus, it will also put you on an emotional rollercoaster.
Find a way to take as many healthy supplements as you can, eat better, go to the gym, go for walks, socialize with friends. Do this for your physical health, but 10x more for your mental health as you are going to have to be mentally strong and physically healthy on this path. For me going out with people i knew or had lost touch with every weekend for a coffee was the best therapy for me, never talking about my situation but just relearning how to socialize. This will help you tremendously.
Good luck and sorry you find yourself in this situation.
