Rowen, I've been trying to figure out what to say to you and I'm having trouble getting the wording right. I mean well, so please forgive me if what I write sounds bad.
When you first told us about Dave, I read the age difference and thought "this is gonna end in tears", but I didn't write it because I really like you and decided to hold my tongue instead. Thing is, the things we're told to avoid in relationships are there for a reason. Things such as LDRs, rebounds, age differences, FWB and so on. We're told to avoid them because the odds of heartbreak from these ventures are so high.
Sure, rule breaking relationships can and do sometimes work out. Heaven knows, I broke numerous rules when I met my now hubby....but the fact that we turned out as a successful couple was far more about good luck than good management. I think that if one is going to venture into a relationship which goes against the rules, it must be done so with a degree of acceptance of the high odds of failure. I guess this is what you mean about "being realistic".
Rowen, as remote as it seems now, you will recover. And you will find new love. You're still young and you're a great guy and you deserve it.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.