True, it is wonderful to make contact with people we haven't been in touch with for a long time. But you are not the same person you were 25 years ago and nor is he.
You cannot recover the past.
Think seriously about why you are dreaming about this person. We often think about what would have happened if... But it didn't and you can't go back to that point in time and see how it would have worked. You can only dream and fantasize about it - but you cannot know. I could have been a complete disaster. You might have split up. Then again it might have worked out tremendously. But it would have worked out because you both put the effort into it, not because it was destined that way.
Think instead about what you have. If you had stayed with the other guy you wouldn't have your three children!
I honestly don't know what advice to give you, because one part of me tells me to do what I feel and the other tells me to treasure what I have! Can I do both?
I have been in touch with my first love for about 25 years now (we met about 5 years after breaking up and have been in touch since). We talk frequently, but we don't want to get back together although we do mention it every now in then, more joking than serious(maybe as an experiment!! to see what would happen). We know how each one has changed and the dreams of the past are past and we both think of our past together as a beautiful experience that ended, caused pain which has gone, caused wounds that have been cured. But getting back together? - no.