1. I don't think anyone goes into a virtual relationship with the intention of meeting in RL. Not saying it can't happen, just that no one really expects that going into a new relationship. I feel like you have to become friends and let it build or not build from there. Later, if both parties are available and want to meet RL, that's totally up to them. If they just want to continue in SL, they can decide that.
2. It' s not for me to say what happens in a RL relationship if one of them has an SL relationship. It depends on how strong their relationship is, how secure the partners are with each other, etc. If an RL relationship is over due to a SL one, there were far bigger problems than a virtual game.