I have a lonely beta fish?

Some bettas are more tolerant of tank mates than others.

You could try 5 harlequin rasbora, maybey 5 cherry barbs

4 kuhli loaches if you have smooth substrate or sand,

or 3 African dwarf frogs.

there are many fish that are compatible as betta tankmates. The four rules that you can use to determine whether a fish is compatible are

1) Not colorful or resemble a rival betta's colors (guppies)

2) Not a fin nipper (Tiger barbs are a big NO)

3) The right size for the size of the tank (No common plecos in a 10 gallon tank since they get to 2 feet in length)

4) Lives roughly in the same water conditions as a betta (no brackish/saltwater fish)

more info here

http://bettacare101.com/tankmates

anything without long fins. Neon Tetras wold be a great choice. Maybe a couple of mollies. Rasboras are a great choice as well.

Stay away from guppies because the betta will tear apart their fins.

I have a pleco and upside down catfish in a 20 gallon tank with a king betta. Never had a problem. African frogs are good, as well.

You can add in Neons or Zebra Danios with your Betta - about 6-7 in a group with the Betta. NO guppies as they look like another Betta with the colorful tails.

Neon tetras would be a good choice. Harlequin Rasboras and African dwarf frogs make wonderful tank mates too. Shrimp and snails are also cool.

Actually, Betta's don't get lonely.

mine's was very happy with endlers and shrimps. Now he is in betta harem with 3 females

Betta fish are solitary animals and should not be kept with any other fish but they can be kept with African dwarf Frogs. African Dwarf frogs look nothing like fish so Bettas do not want to attack them.

How do you know it's lonely?