I know, as a guy it's my job to be the emotional rock in a relationship.

I don't lose my cool often but I find my natural defence mechanism when she does something I don't like, is to go cold on her.

For example:
We're talking and she tells me she wants to change our plans.
I find myself saying 'Okay, that's fine' (To not come across as needy), but I then go cold on her after that.

She might ask me 'are you okay?' I'll respond with 'I'm good, why?'.
I'll brush it off and we'll move on.

Is this AFC behaviour?

I'm just trying to stay strong in the relationship and not blurt out my emotions to her.

I really need some advice in maintaining a good frame in a relationship.

Thanks guys.

It isn't your role to be an emotional rock.
It is your role to not have emotional outbursts.
If you dislike something badly, talk about it. Explain it in a simple way why you feel that way... don't just start argueing and throw in old-problems or something similar.
That way she will understand (if she is intelligent enough) and you might not have it again in the future

Thanks for the advice man.

Any more tips?

Yea you want to be cool and confident but communicate when things dont sit well with you. Trying to lay a girl and dating are differnt from a relationship, a lot of rules dont translate well.