If you're looking for a meeting place or a good stop around ½ or halfway between Ashburn and Boydton, you can try Richmond, VA, which is almost 2 hours south of Ashburn, or almost 2 hours northeast of Boydton.
Other possible places to stop near the midpoint include Golansville, Houstons Corner, Doggetts Fork, Laurel, and Tuckahoe.
About ¼ or a fourth of the way, you can stop at Fredericksburg, VA. This is almost an hour south of Ashburn.
About ⅔ or two thirds of the way, you can stop at Petersburg, VA. This is a little over 2 hours south of Ashburn, or a little over 1 hour northeast of Boydton.
About ¾ or three fourths of the way, you can stop at Borthwick, VA. This is about 2½ hours south of Ashburn, or almost an hour northeast of Boydton.
If you drive straight through without stopping at all, the total distance is 225 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 3 hours, 29 minutes.