A few things.
1) Rondo is gone
2) Rondo is not the player he once was
3) Rondo unique strengths/weaknesses seem to really limit what teams he can work well on
4) We were playing pretty poorly when Rondo was here
5) We are playing some really nice basketball since rondo is gone, and I love our current guys
Despite all of the above, it's still very hard for me to see Rondo in another uniform.
Basketball is a business of course, and for business reasons Rondo had to go - he didn't fit well with the group of guys that were being put around him, his career position didn't suit the (likely at the time) lottery aspirations of the team, and his personality was probably a bit hardcore to put a group of young prospects around.
Trading Rondo was a move that made the most sense for both parties, but it still hurts. Thinking back to all those moments with Rondo, Pierce and KG celebrating together...thinking of all the headaches he gave Lebron's teams over the years as a triple double machine...thinking of all those insane passes he used to make (one of the only players ever who made a pass as impressive a highlight as a dunk!).
It's actually sad for me seeing Rondo struggle the way he has in Dallas. In one way as a Celtics fan it makes losing him hurt a little bit less, but in another way as a Rondo fan it makes me sad to see he's not finding success and that he's copping so my flak.
Rondo was one of the last in a line of true, old-school point guards who score 8 points and still completely dominate a game (a series, even). There was point in time when you make an argument that Rondo was the best PG in the NBA, and people wouldn't laugh at you.
I hope he one day recovers that form.