Honestly, you should be GRATEFUL that he told you this upfront.
And in case you're new to dating, it's very common for people to date multiple people at once. Dating does not equal exclusivity. Be happy you found this out before you fell for him and thought you were the only one.
With that said, keep dating him if you're feeling him. And while everything might be "great" with the other guy, he's clearly missing something. Otherwise he wouldn't have went out with you.
Good Luck
