Why is my mouse biting himself :/

Pippin! He's an otherwise healthy "fancy mouse" with straight fur, probably about four months old. Very active and inquisitive, normal appetite.

Well the only problem is that hes has been biting off his fur into a large patch on his side and a few other small patches and he appears to have bitten a small wound.
He obsessively cleans himself and bites at the fur on his side and it has caused a small cut about 1/3 the size of his paw. It was scabbed over when I noticed. Is there something wrong with my mouse? Pippin! Can someone help?

It's an obsessive-compulsive things some bucks get (OCD), often out of boredom or loneliness. The way to get him to stop is to distract him. Give him a spinner, lots of toys, and take him out and play with him often.

Okay well all the above symptoms are still continuing. I believe he just needs friends. What would be the best way to introduce a friend? Male? Female? It's really making me sad and I regret not having a friend with him from the beginning. Oh poor Pippin!

You are in a quandary. Male mice do not get along with each other. They will fight over territory and hurt and sometimes kill each other. If you put a female in with him, he will probably impregnate her and you will suddenly have more mice than you want.

Male mice have been known to get along very well with tame female African Soft Fur rats (which are technically mice). Best thing you can do is find an ASF breeder. Be very careful when you do the introduction in case your ASF for some reason attacks your mouse, which can happen. I do introductions with the mouse in a plastic exercise ball. They can see each other and smell each other through the air slits. ASF's are loving and devoted companions.

Sterile does and hermaphrodites also work as companions for male mice, but are rare as hens' teeth.