I hesitate to support a diagnosis of social anxiety. It sounds to me like you are discouraged.
You are certainly not alone in your situation. The older we get, the harder it can seem to make new friends. People do have established circles of friends. Those with adult children are often wrapped up with the grandkids. It’s not likely that you will meet new people as you once did through your job or through your children. Complicating things further is that you have a partner who is happy with you as his only real friend.
But please don’t give up. You can find new and interesting people to spend time with. The solution is to find an activity that you feel passionate about. It could be a political issue, a charity, a sport, a theater group or bird-watching — as only a few examples. It doesn’t matter as long as it is an activity that attracts other passionate people.
Get involved. Focus on making a contribution. By working together, you will get to know other people who share your interests. Putting your energy into making a difference takes the pressure off the longing for friends. And — you know what? — Friendships get made that way.
Please don’t let your partner’s contentment with staying home stop you from going out. If anyone is tactless enough to hassle you, simply tell them that “oh, he’s a homebody” and change the subject. You are not required to be attached to him with velcro. If you are comfortable with yourself, other people will let it go.
I wish you well.