I do not usually begrudge players who leave the Sox and sign elsewhere, even if they sign with the Yankees. I understand the business aspect of free agency. I have no problem with Ellsbury in that regard, other than the fact that he's a stinking Yankee.
However, as you said, Boggs riding the horse was a dagger through my heart. Damon stated that he could never sign with the Yankees, then turned right around and signed with them. It was like he ripped my heart out and stomped on it. Clemens is up there too in the heart breaking category, though for some reason, he doesn't bother me quite as much as Boggs or Damon.
Anyway, those 3 are dead to me. Yes, I take it personally. As the saying goes, "Hell hath no fury like a woman scorned."