A bigger picture.

Look, we had our good days, the happy times, but they are fading away. Sooner or later, I will hate you and trust me, that feeling is going to be mutual.
I shall not deny that you are a pretty great person, and so, we deserve better. Yes, when I told you my decision and reason, it may seem ultimately the most selfish thing to do, still, I am crazy sorry that this is more than you and I can take. Pushing it to the limit is, really, NOT a good idea.
It is a difficult compromise, but that is all to it.