mgp744, I think just by being a good listener you can help a teenager a lot. Maybe try to remind and praise them of all the things they're doing right. Teenagers react pretty badly to negative criticism (e.g. "you're obsessed with this boy"), so when the opportunity arises, try and remind them how much *they* are accomplishing (as opposed to how much their boy/girlfriend is enabling them). I think in puppylove teens tend to fuse their identity with that of their partner, and fail to see where they are capable independent beings (because they don't yet understand that love includes being a capable independent being). Over than that, I hope you don't get overwhelmed with all the highs and lows of the dramatic teen relationship. Hope this helps!
The feeling you are talking about is the new relationship feeling. I have been married for over 17 years but that being said when you are a teenager it is more of a puppylove. You now as an adult will find out that relationships will be different as being older you need to look for more in a person that that cute look or babyface. The adult world is more complicated but guess what it is an all new world so enjoy and don't worry about getting too deep too quick enjoy the experience and the person. I hope that you don't prejudge the person as this is what makes a person have problem relationships not that you do but please look for someone you can talk to and enjoy being around first and the relationship will happen it is is meant to be.
Its totally normal to experience those feelings and emotions everytime you get into a relationship. How long have you been dating this person? Usually those feelings will go away after you begin to open up to the person and you become more comfortable around them. It takes me usually 2 months to actually feel comfortable, but I dont fully open up untill around 6 months. The whole "I'm not even good enough for her/him" could be insecurity. Insecurity can come from many reasons. Someone could of made you feel insecure by making comments toward you, etc. Just be yourself, and enjoy life, and have fun. These feelings and emotions will go away after awhile. Hope this helped.