I don't know you John, you sound like a nice guy but.......... If my daughter was 14 dating an 18yr old, I'd take him to the barn where we could be alone and give him 2 choices...to leave with all body parts or carry(with his remaining arm) most of his body parts in a feed bag!
If her parents let her date 18 & 19 yr olds, I think they have a problem. When you are both in your 20's (20-24) I wouldn't have a problem, but 14 & 18 I have a serious problem.
I mean no disrespect to you John, but being a bit older having kids I realize and see things differently than when I was 18.
Be there as a friend with other friends/relatives around. NEVER be alone with this GIRL! You could get in a big pile of trouble wheather it be true or false.
Take care John and be careful!