You can be happy living with Arachnoiditis, but it all depends on you. Your lifestyle is DEFINITELY going to change. You won't be able to do many of the physical things you used to do, including housework, shopping, even personal care in some cases. You need to be aware of your limitations, don't overextend yourself, and ASK FOR HELP if you need it. You also need to find other activities you enjoy that are less taxing on the body, or find ways to do the activities that don't hurt you. For example, use a motorized cart or walker when shopping. Coach sports instead of playing them. If you enjoy travel, take shorter trips. Ask for assistance at the airport. Develop new, less strenuous hobbies and activities. If you want to work, try part-time or work from home. Get help with the housework or personal hygiene from family, friends, or agencies (there are many out there). Rest when you need to.
The main thing is, HAVE A POSITIVE ATTITUDE. You're just disabled, not dead. Don't have an eternal pity party. There are still people in this world who have it worse than you. Your life can still go on. It's just a new chapter.