Boy did I get one today.

I have been riding by myself for the past 4 or so months, and have made some pretty good gains getting used to riding again, as well as losing over 35 lbs. I picked up a new road bike for the first time in around 20 years, getting off the mtb I had been riding as a hybrid. My average speed jumped up by well over 2mph right away, and has been much easier to log miles. Over the last two weeks I increased my average speed almost a mph just on the road bike alone.

The area that I live is pretty hilly, I wouldn't go so far as to say climbing mountains, but the whole terrain is rolling rather than just flat within several miles of the house. It is great for training rides, and getting used to what may come just riding down any given road.
A good friend of mine, who is also 17 years my younger, was heartened by watching my progress and had been on the fence about riding himself. He went last week and bought a road bike that is in all respects the mirror to mine as far as weight, group, etc. just a different manufacturer. He has been riding with a partner, his brother, who is an accomplished long time cyclist, and even before he was riding has been into working out, eating healthy, etc.

We had been talking for the past few days about going on a ride together at a PATH Foundation ride up at Panola Mountain. We got together today and headed up there. The terrain is much more hilly even than the area I live and have been riding. There were two hills that were as steep as the steepest around here, and easily twice as long.....I had planned on riding 15-20 miles today. I have been "training" on 10-15 miles rides, gave myself some good rest yesterday and headed out.
Three miles into the ride, I was dying. My lungs and legs were burning like crazy, and I was just watching my buddy fade away. He eventually slowed down from his pace to stay back with me, and honestly if he hadn't been there to motivate and push me, I never would have even completed the ride. I have never sat down in the middle of a ride, and over the 13 miles I managed (or I should say that he managed) to pull out, I had to sit down on a bench twice. Even my own average speed was a great deal slower than normal.

So, to get to the point....I will likely continue to be riding alone, at least for the foreseeable future, all but one or maybe two days a week. That will be after I have attained the goal average speed I have been thinking to make. After the ride today I just don't see that happening within the time frame I have set at my current pace.

How do I go about motivating myself to push that much harder, outside of the comfort zone? Especially while riding solo?

I realize that speed isn't going to come back or develop overnight, and that I am almost 20 years older than I was when I rode regularly before. I just don't know at what pace, and how hard I should be pushing myself. Going fast when I was 20 was just easy, I didn't have to "train". I rode bikes from the time I can remember, and it is all I wanted to do. The being in shape and advantages that came from it were totally taken for granted.

Today was a real eye opener. It is going to require a whole lot of hard work and dedication to make the goal I have likely prematurely set for myself.