A sentence like 

> 
> **We've known each other since 2015**
> 
> 
> 

sounds common and normal.
However, could you **explain the possible circumstances** of using a sentence with **2 Present Perfect clauses linked by "since"** of this kind: 

> 
> I've become suicidal again **since** I've worked here  
> 
>  I've been feeling down **since** you've been gone
> 
> 
> 

I think I can somehow feel the meaning but I'd appreciate a native speaker's advice.  

With regards,  

Anabel