I wouldn't say he was forced to reject Kallen.
It's not like they were lovers torn apart.
There's no evidence to support that.
I think it's obvious she was his friend, he just didn't want her to die with him, and that was because he wanted her to live her own life.
It's like when there's a girl that really likes you, but you don't like her, you let her down easy and tell her that you're just not the guy for her.
Also, CC didn't want to die.
Her wish was to be truly loved by one person due to the fact that her Geass made everybody love her falsely.
In episode 15 of R2 (C's World) we see this clearly.
So as we can clearly see in the anime, CC's true wish wasn't to die, it was too be loved.
Suzaku did want to die, that's a fact.
However, even he didn't want Lelouch to die, but Lelouch insisted.
I believe that was made clear in Okouchi's Mutuality Story:
http://bwys.org/downloads/oneshots/C...ality_BWYS.pdf
Therefore, while it is clear that the ending of Code Geass (the Zero Requiem) was a bunch of malarkey, it is also clear that the ending was a jumbled mess.
As a writer, artist, and now publisher I can tell you that when you have a large number of people working on a project the story tends to get pulled in a multitude of directions.
Code Geass clearly suffers from this.
It is amazing that the show was as popular as it was...so Kudos to Okouchi and Taniguichi for pulling it off as well as they did.