chewing is a process where upper & lower teeth come in contact with each other & help in churning the food. so when the upper wisdom tooth is removed, then the lower tooth will not help you in chewing, instead if you keep that lower tooth for many years then it might harm its adjacent tooth because of occlusal drift.
occlusal drift means that when the opposing tooth is absent, the tooth slowly starts moving up.this will probably take few years, so if you can't afford the removal right now then you can get it removed even after 8-10 months or even an year.
For the pain which you are having, usually after wisdom tooth removal pain persists for about a week, but in few difficult cases pain will be there for about 10-13 days. It is a good thing there is no swelling. the dull aching pain will reduce as the healing process slowly completes. But if you are having pain even after 15 days then you should get it checked with your dentist
For better & fast healing keep that area very clean, you can also use hexidine mouthwash for relief.