It's about state of mind. The word 'yoga' actually means 'to yoke' and it refers to linking your unchanging awareness (some traditions call this your soul, your spirit, your higher self. Yoga calls it your cit (pronounced chit)), with your psyche (ego/citta (pronounced chitta)) so that you can live with awareness and make helpful, not harmful, decisions.
So: 'shall I eat that chocolate?' would be a decision based on our irrational, and changeable egos if we said 'yes because I feel miserable' or 'no, because it'll make me fat'. If we linked our cit with our citta, we'd be saying 'no, because I'm not hungry' or 'yes, I'm hungry and I need an energy boost' - it's a wise decision instead of an ego-based irrational one IYSWIM.
Yoga uses various 'tools' to help learn how to do this, and one of those tools is asana (the postures). When you're linking your breath with your movement, it leads to you stilling your chattering ego psyche bit so that you're listening more to your higher self/soul bit. You're feeling every bit of the movement and listening to what your body's telling you.
The idea is that the asana are preparing you for a period of pranayama - seated breath work. This is very similar to Buddhist meditation.
So, no, you don't have to become vegetarian or anything, but many yogis do because they begin to feel that it's a harmful decision to eat meat when there are other choices that would be less violent. I am semi-vegetarian. I try to eat very little meat, but I'm realistic in knowing that I can't make a change like that overnight, so I try to eat with awareness instead.
Practising yoga is literally that - practising. It's not doing a few exercises in the morning to get bendier, it's practising linking your awareness with your psyche so that, as you get more and more practise, you begin to feel it seep into the rest of your life so that you're making wise decisions all the time.
Western yoga is often very ego based, even though most Western yogis will deny this. Otherwise, why all the photos of terribly bendy, skinny, beautiful women? why do we feel that we need to be able to do crazy backbends on our heads in order to be good at yoga?
Actually it's not about that, it's about learning about how to work with our bodies and our psyches to challenge and find our limits and start where we are and make helpful decisions etc.
Does that help?
You probably don't need a yoga weekend - I suggested that as it sounded like you couldn't get along to a regular weekly group.