Is he flaring? If so, is the tank lit? If so, he could be seeing his reflection and attacking it... flaring at themselves tends to happen when they aren't quite used to their reflection in the tank wall when the light is on. Try turning the light off and turning it on in short periods to let him adjust and let him understand that it's only himself that he's seeing.
Betta's really don't get lonely, while you could add a bottom dweller, I really can't see that helping him any.
Beyond this, I really don't know what else to tell you. Try the light and maybe that will calm him down. Test your water parameters, if nothing else you'll have an idea of the water quality, which may or may not explain his behavior.
Did you use a water conditioner to remove the chlorine from the tap water? Technically the tank should run for 24 hours before adding fish, but sometimes when we get anxious we put fish in a bit early .... I do know how it goes.
Is the tank cycled? Do you know about the Nitrogen Cycle? If you do not then you need to read the following...
The above article will also give you an idea of the basics of taking care of your betta and his wants. They are "people fish" and will be much closer to you than any other fish. They do not know they are fish and do not really like the presence of the other fish and will hurt or be hurt by other fish usually because they are not used to being with them. It really is better to let them be alone.
Please be welcome and browse through our section and get to know us and see how much information there is here and ask any questions you may have. The forum is all about people helping people with information. There are no dumb or unnecessary questions so please ask if you need to know something.
Welcome and let us know if your fish has a name as we do like to address them by name if possible.
Does he have gold specks on him if you turn out the lights & shine a flashlight on him? what are you feeding him? bloodworms, thawed frozen peas minced and daphnia are betta favorites as far as i know. Is it a particular spot (like the side or by the filter housing) that he's banging?