Alone, you're doing a great job. You've been spending your time on GAL activities and giving your W space. The contact you initiated was business related and you kept the meeting short and to the point. All excellent.
You may feel bad now but you're right that you would have felt worse if the conversation were dragged out and eventually ended up back on R issues. Your vindictive part is natural and normal. And that's what you're trying to accomplish here - showing her what life alone will be like and letting her decide if that's really what she wants.
If you feel bad for continuing in this manner, try looking at it from a different perspective. There were problems in your marriage, enough that your W felt overwhelmed and that she needed to escape her life and live out the fantasy of being single and carefree. By removing yourself from her life you are removing yourself as the person to blame so she has no choice but to look at herself and the situation she has created. This gives her a chance to gain some clarity. You are giving her the gift of NOT solving her problems for her.
No one said it would be easy. But you can get through this. When I was feeling down I called a girlfriend to chat about anything other than my sitch. Since you're a man I'm going to assume that you're not a big phone chatter. Do something fun and/or indulgent, you definitely deserve it!
If you love somebody, set them free. http://tinyurl.com/2empx2g