is this the start of something cuckold-like?

Hi!

So this happened to me today, my gf woke me up,got me hard (very fast) and started riding me.
She came pretty fast(haven't had sex with her for a while) and right after it she said "you won't me cumming today" and left.
I didn't cum while having sex with her, i guess that's important to mention
Does anyone think this is a start to chastity or something?

Without knowing your girlfriend, it's difficult to know the reason for her behavior. Maybe she's in a bad mood and felt like taking it out on you. Maybe she just woke up after dreaming that you fucked her girl friend. It's best to just ask her what's going on.

I don't think it's a cuck thing.

I think she wants you to be horny all day so that you really go at it at night.

Yes... most likely she just wants you horny, but it does give you oportunity to start talking about her cucking you. Take advantage of the situation and suggest she do that more often and maybe even other stuff. Have fun with it.