Hi Emmalouise
It is quite common for people after a lower limb orthopaedic injury to have a reaction so that the normal function of walking is disrupted. Some people actually seem to "loose" the "motor program" in the brain for walking and just can't make it happen. In fact it isn't really lost. As you are probably aware this is a much to do with psychology as a physical thing. In your case it sounds like it is a bit triggered by anxiety about the healed fracture failing. A traumatic fracture can be quite a shock and you may have lost confidence in your body to do what it should do. Sometimes there is a pinch of reality in that fear if the fracture hasn't healed so well but if the orthopaedic surgeon thinks it is ok it then it is most like to be safe as houses.
It doesn't mean you have become a space cadet this can happen even to the most stoic and robust of the human race. So don't worry, it does pass. The best thing to do is to get a good physio (chose one with a rehab background is a good choice) to help you get walking again. You may find it doesn't take many sessions but it can be very reassuring. I think this would work much better than trying to describe what to do over the internet. The physio can assess you properly and will know about your injury and what you can safely manage and how to progress your exercise.
Has the wounds from the surgery all healed up and do you like the water? If so hydrotherapy is a great treatment to get you going. You can work on strengthening up your muscles safely and can practice walking in the pool which reduces the weight through the leg but still gets you going. You can progress this to resisted walking and in even try jogging etc. Physiotherapy hydrotherapy pools are warmer than swimming pools and that can be a great place to start.
So get some help. That is what physios are there for.