Hi, I'd like to help you with your question.
I am sorry you are going through this with your marriage. It is difficult to be separated and not be able to get answers as to what is going on.
There may be many reasons your husband has chosen to be separated. He could just need time to sort out how he feels about the marriage, he could be doubting his abilities as a husband or as a person or he could want to leave the marriage but doesn't know how.
Men also experience a mid life hormonal change similar to women's menopause. It is not often talked about and causes changes in men they may not be familiar with. This could also be part of what is happening with your husband. There is a good article about it here http://www.webmd.com/healthy-aging/guide/midlife-crisis-opportunity.
As for what you can do, there are options. First, when you see your husband, do not bring up the marriage. Speak with him in a nice and kind manner and do not cry or get upset. Talk about general topics and keep the conversation about fun and interesting things. If he brings up the marriage, go ahead and discuss it. But keep it general with no accusing.
Be strong and self sufficient. Take care of yourself and the home. Pay bills, keep the house up (hire help if needed) and generally live your life. Go out with friends, pamper yourself, and keep yourself busy. Let him know that you love him but that you also don't need to lean on him all the time.
Do not bring up the marriage problems unless he does. Let him have the time he needs. However, when he does bring it up, suggest counseling. You can get a referral from your doctor, local community mental health center, or if you attend church, your pastor can help. Pastors are often qualified counselors or they can refer you to a therapist.
There are also some books that may help you. One is called Hope For the Separated: Wounded Marriages Can Be Healed (Chapman, Gary) by Gary Chapman. Another one is Should I Stay Or Go? : How Controlled Separation (CS) Can Save Your Marriage by Lee Raffel. You can get these either on Amazon.com or your local library may have them for you.
Hang in there. Marriages often go through tough times. But your marriage will be much stronger once you come through this.
I hope this helped,