"I do not love you."

Even worse, you can say "Jag älskar dig inte."

With pronouns, both orders are possible. So you can say Jag älskar inte dig and Jag älskar dig inte. With nouns, you can only have the noun last Jag älskar inte Björn.
Jag älskar dig inte is a more neutral way of saying it. Jag älskar inte dig implies that I don't love you, but I do love someone else.

er is the object form of ni, and dig is the object form of du.

'du' is you 'er' is y'all

The thing is that the verb needs to be in the second place in all sentences (except questions and subclauses). This is why inte usually comes after the verb, but it doesn't have to be, it's just that we very rarely want to start the whole sentence with inte.

du is the subject form and dig is the object form, and the thing you love is the object.

In English they're the same for this word, but you have different forms eg. for I and me – you wouldn't say You don't love I.

ej is a formal version of inte which is basically never used in speech, but often on signs.
About the word order, read under 1.2 here: https://www.duolingo.com/comment/8970470

The difference is whether it refers to one or multiple people.

Du/dig = singular you (thou/thee)

Ni/er = plural you (y'all)

"Gör" is more like to physically do something in Swedish whereas in english its just a placeholder that means nothing