I think that if you can do it, you should carry on as you have been, but avoid any OR talks- just listen and validate when he brings anything up. He's obviously confused, and I think that he's not in a place yet where he can date and then joke about it; for him it's something a bit scary (for whatever reason), so being there and fun with no pressure is probably a good way to go.....you just need to keep on enjoying your picnic.
I hope you're OK otherwise. This must be so tough to deal with on top of the news about your Grandad. ((((Michelle))))
L.xx
Walk on, walk on, with hope in your heart. And you'll never walk alone.