There's been a few great threads on this question already that you might want to check out including:

What were the motives for the assassination of Julius Caesar

Why was Julius Caesar considered a Tyrant and how did he bring about the end of the Republic? by /u/LegalAction and /u/XenophontheAthenian

This thread also talks about it.

I'd like to see some new answers on this though cause most of these are fairly old.