Enid: You sound a lot like my husband! He's much better now, but still not one to start a conversation with someone he doesn't know well. It was so bad that at one point my parents had a 'talk" with me when it became apparent that this was more than a casual relationship.
Talk to your "daughter" (yes, anyone who takes on the role of mom get's the title!) and ask if she'll "warn" him. You obviously can laugh at your own personality quirks - it'll help if you find yourself in that awkward spot when he's there to be able to say "hey she warned you I'm not good small talk! lol".
How neat that she think enough of you to introduce you. trust me - he's more nervous than you are.
Try not to stress about it. It is what it is - and she knows you and is bringing him anyway

- she wants you two to meet. Enjoy the visit.
Just a suggestion: can she tell you anything about him - his hobby's, job aspirations, interests? It might help you "plan" topics you can fall back on if you feel the need.