When a marriage comes to an end there are all sorts of changes we must adjust to. We might move, even if we do not want to, we might lose family connections we had through our spouse and we might lose friendships. Most married couples have mutual friends, usually families and couples, and quite often these side with one of the married partners and drop the other or drift away because they feel awkward about seeming to have a favourite or take sides. Losing your partner can be one of the loneliest things to happen to you, but when you lose friends too life can become very lonely indeed.
You need to give yourself permission to be sad and thoughtful for a while. It will take time for you to get over everything that has happened and adjust to your new life. Sometimes this is done far better if you do it alone and keep your thoughts to yourself. If you have a friend that you can talk to who can keep secrets and does not blab about what you say to everyone then talk to your friend but otherwise be careful who you confide in. Most people cannot really help and end up just being nosey when they listen to you talking about such things. It really is none of their business. It is probably best not to confide in someone you have not known very long, or who is quite secretive with you or who you only see now and then, as it may backfire on you later. By becoming your own best friend you are going to find that life is less lonely anyway.
Then you need to find a way to make some new friends, friends that are your type. They may well be different to the friends you had before. Now that you are single it may well be better to have single friends rather than families or couples. Some women do not like being friends with single women as they see them as a threat to their insecure marriage (which says a lot more about them than you) and you may also find that husbands of friends will try it on with you now that you are single. But you need to be selective and carefully sift through all of the potential friends that are available to you and only choose the ones that are going to enrich your life. Do not grab on to anyone and everyone simply because you need more friends.
The best way to find new friends from scratch is to meet people through your interests as it is best to have friends that you have things in common with. So join classes or groups that are connected to your hobbies and interests. If you have this in common with your new friend to start with and then find you have other things in common with them, hopefully, later... you will have a solid basis on which to build this new friendship.
Instead of feeling sad about the friendships that have died along the way tell yourself that you are starting a new life and this is an opportunity to get rid of disloyal and unsuitable friends and replace them. Set yourself a target of a year in which to make some new friends. Go to places you might not normally go to in an effort to meet these people. At the end of a year you will find you have a better circle of friends than you did when you were married.