Could he have an STD? *Short*?

That's great that you are waiting. Since you value yourself and have waited all this time I would only expect the best, and this guy, no matter how great he sounds can only be trouble. Listen to what your heart is telling you, you said that you think about it all the time, right? Go with that. Let your 1st time be with that special person not some one who was with your sister. Please. I know many don't think its right to wait till your married but that's my views. If you have waited this long then you can wait longer and be 100% sure. I myself would be very worried about STD's. He could have them and not even know about it, many guys don't have symptoms. Just don't rush into anything now. That's a lot of partners for his age. He may move on after he gets with you, and then you waited for nothing! I hope this was helpful.