This is purely for a situation where i have already met the girl twice before.

1st, she came into my work. I said i will come into her work next time. She said 'cool' and invited me.

2nd, i came into her work (coffee shop) and ordered something. Talked a little, joked around then left.

Seems to be some interest there.
Can i ask if she is single/seeing someone, if i am going to ask her out straight after if she says "Yes"?

She is a few years younger than me and i have already met her before. I plan on asking her in a very casual way during a conversation.

seems to forward if your asking if shes single......... does it matter anyways if shes is or not ;)

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Life is what you make it;

You can try to assume that she has a boyfriend and use it in conversation. For example:

HB: Tells you some silly recent story about her
you: "Haha, that's awesome! What did your boyfriend say about it?"

She will either tell you or say that she has no BF. You will have your answer and avoid possible awkward situation after direct question

Most women are in some sort of a relationship but that doesn't mean that they're in a relationship with someone that they intend to stay with. The book "The Myth of Monogamy: Fidelity and Infidelity in Animals and People" does a good job of explaining why that is. Women tend to grab ahold of a man as they look for the man that they want.

You're better of saying my friends and I are going to XYZ Place tonight you should stop by.

if she walks in to see you or you see her just say "so why do you like to see me and not your bf?"

mR.e

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dont even think just do it!

Just ask direct and when she says I have a BF , just act cool and say I'm not asking you to marry me , I just wanted to go have some drinks.