Decírtelo (en. Tell you)

/deˈsiɾ.te.lo/

Slang Meanings

To express something bluntly
When I say I need to tell you, it's because I want to say it to you bluntly.
Cuando digo que se lo debo decir, es porque quiero decírtelo sin rodeos.
To tell you what I think
I'm going to tell you everything because we are friends.
Te lo voy a decírtelo todo, porque somos amigos.