-1
In this sentence, which answer is correct?

1. She has a boyfriend who she loves.
2. She has a boyfriend whom she loves.

Or should there be a comma?
And what are the rules for who/whom?
Thanks in advance.
+1
The object case of who, whom, is disappearing, as many old inflections in English have done over the past few hundred years.

It is still always used in a prepositional phrase:
She has a boyfriend with whom she lives.

Except if the preposition is at the end of the clause:
She has a boyfriend who she lives with.
Who did he give the ring to? (informal)
To whom did he give the ring? (very formal)
Comments  
Whom is grammatical, however I think modern day grammarians accept even who here.
Somehow the sentence sounds a little odd to me.
I would say "She has a boy friend and she loves him."
Students: We have free audio pronunciation exercises.
 AlpheccaStars's reply was promoted to an answer.
Rainbowwalkershould there be a comma?
Here's the contrast between using a comma and not using a comma.

She has a boyfriend who she loves. (And she has several other boyfriends who she does not love).
She has a boyfriend, who she loves. (She has a boyfriend, and she loves him.)

CJ