It's great that XW is spending more time with you and the kids as a family. Build on that and don't focus on dating right now. Don't bring up dating for the next month.
How about snatching some "date" time without her realizing it? When she's over, get the kids into their own activity - rent them a video, or get some new coloring books and crayons or play dough - then you have some "alone" time talking to XW - about anything except your R. After the kids are in bed, take out a video you rented and invite her to stay and watch it with you. Once she's done that, then see if she wants to go out to the movies.
Use Mother's Day to your advantage. Ask XW to go to church as a family. Take her out to eat, or cook for her at your place. Have the kids make her cards or pictures. Give her a card from you thanking her for being the mother of your children. Give her a flowering plant from the kids. (She'll think of you everytime she waters it!) Take the family to the park - go on the swings, the slides, blow bubbles, etc. - just hang out with XW and kids and enjoy.
Don't go to that party. Give her space. You are still the pursuer and XW is the distancer. This is your chance to turn the tables and give her the freedom and independence she wants. Show her that you've changed. If she goes alone to the party, she'll be with other couples and she just might miss being a couple - with you.
Your glass is half full, not half empty! I know how difficult this has been for you. You're the fisherman and she's the fish. She's taken your bait and you've got your hook in her, but you're trying to reel her in too fast. Don't let the fishing line that connects you get broken. Take it slowly, one revolution at a time. Slow and steady wins the race.
