What you're saying is normal behavior. That's why they're called fighting fish, they will go after their reflection or other fish. Some would argue to just leave the fish by themselves; that they're happier that way. In a 5G you could try a couple snails or 2 frogs (I think people use ADF's). The thing with snails is that if you get a male and female, they will breed like crazy and you'll end up with lots of baby snails.
If your betta is very aggressive and starts attacking them, than you'd have to bring them back. I don't have any tank mates for any of my fish, they love being by themselves, but it's up to you. Some like the company and some would rather be by themselves.