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"Those actions backfired harshly when his jealousy became a gripping anxiety, a constant belief that I looked down on him and sought the affections of better men."
That's because you did. You were bored, the love was dying and you wanted to break up with him.
If you pushed him away until he moved out, it was a pretty ugly situation you helped create. He didn't leave "out of the blue" - one or both of you was avoiding confrontation or refusing to pay attention.
"That this broke my heart is almost appalling to me, because I just know that he and I are not right for one another."
As Cary points out, breakups hurt even if they were necessary and what you wanted.
You seem to resent that feeling guilty, but if you treated your boyfriend as your ex treated you, your guilt is based from understanding how unfair it was.
What Cary won't say is you need to get over yourself a bit and learn from this.
The letter reads a bit like you want to blame something else besides yourself. Self-justification is not the issue. Breakups happen and quite often there's no right side. It's going to hurt but then it won't.
Instead of trying to find blame, think about what you learned about yourself and your likes and dislikes. This might help you be more honest about compatibility before you choose to live with someone.
Also, if you live with someone and are aloof towards them for more than two or three days, they are going to feel hurt. Getting the cold shoulder from the person you live with can be very upsetting. It sounds like you put your feelings first and made him feel bad for feeling otherwise.