You can meet people outside of this group by asking to be introduced to the group member's mutual friends. From what I've experienced and seen with groups, not everyone in each group hangs around with the same people all the time.
When you make it clear to the group that you'd like to meet some more people (but emphasise that you value being in the group, or they'll feel you are ditching them), they'll likely be more than happy to help. Plus, if you allow your mutual friend to do the introduction, a lot of the inital awkwardness is gone because 1) you won't have to approach them yourself and 2) you already have something to talk about (the mutual friend).
As for knowing how to keep a conversation going, look for common experiences. If you are at a friends house, ask how they know the mutual friend and share how you know them. Comment on the party and the general atmosphere. Take an interest in the other person's life and try not to focus too much on yourself...this is a surefire way to keep their attention.
I also agree with the other posters...treating girls, especially if you're attracted to them, like any other guy friend and asking them the same questions is a good way to approach things. Personally, as a girl, I keep a heavy guard when meeting other men as I don't like the feeling of being hit on or having a guy hinting he is attracted to me upon the first meeting. Other girls feel the same way.
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Given a “tentative” diagnosis as a child as I needed services at school for what was later correctly discovered to be a major anxiety disorder.
This misdiagnosis caused me significant stress, which lessened upon finding out the truth about myself from my current and past long-term therapists - that I am an anxious and highly sensitive person but do not have an autism spectrum disorder.
My diagnoses - social anxiety disorder and obsessive-compulsive disorder.
I’m no longer involved with the ASD world.