as/because/since

[Topstudent]

I'm trying to write a dialog:

...He flirted a lot. I didn't know whether I should read anything into it as/because/since I knew he was married.

Are 'as', 'because', and 'since' all correct and natural here? Would one of them be more natural to use here than the others?

 

[SoothingDave]

"Since" is better for me.

 

[jutfrank]

Yes. No.

 

[emsr2d2]

@Topstudent At the moment, you have a monologue, not a dialogue.