I've heard a few places that the way to get over someone is to get involved with another. And then you hear the opposite--not to fall on the rebound. Right now I can feel happy when I'm with someone else, but the minute I'm away from them (and occasionally while I'm with them) my mind and heart goes to my H.

Right, because the other person serves as a pleasant distraction. That's why some say "the way to get over someone is to get involved with another"... but again, it's only a distraction! Just like the OP is to the WAS. And if it's a bad relationship, getting involved with whoever happens to be there, then it's disastrous to get stuck in that off the bat. Hence the advice about rebounds. Better, I think, to get involved with groups of people at first, rather than dates. Make friends, rather than new lovers. After all, the next person isn't the answer, he or she should be the addendum.

The man that I am currently speaking with is actually older than me...and almost 20yrs older than Dave

Speaking as an "older" man who happens to be in that age range you describe (though kicking and screaming all the way!), my perspective is an older guy might be more able to have the kind of relationship most women seek. There's the acquired life experience and its wisdom, the letting go of immaturity, the appreciation for a woman, for something better and the willingness to keep it like that when and if it happens. Took me a while to get there, but I think I'm there. And when women speak with me and get to know me some, they get that sense of difference. Sadly, that might apply to the OM in my sitch, as he's another 8 years older than me. Oh well.