Sorry, but a 23 year old has no idea what he or she wants out of life - hopefully this is just a "hey I really like this guy and I think you guys need to meet since it's serious enough that your paths will inevitably cross anyway" kind of thing and nothing more (e.g. "hey, we're expecting!").
At that age one is old enough to make really bad choices and be stuck with the full ramifications of them as an emancipated adult. Sorry but that's reality. You've done your part preparing her and she's on her own now... You've got to accept that. Now here's the upside - we all went through that "stupid" age and survived it. Some of us actually made good decisions (by accident mostly) and some of us didn't (and paid for it) but we all survived. I'm sure your daughter (who is now an emancipated adult - don't forget this part...) will do fine and even if she makes a bad decision now, she'll survive it because of what you did for her as her dad.
All the best. I truly hope he's not a tatted-up, sideways hat wearing, pants-down-to-the-ankles-showing-underwear retard, there are far too many 20-something guys who are these days. If he's not and is a decent, respectable guy then give her a big hug and tell her you're proud of her judgement.
Good luck, hope it goes well.