dude...hehe
firstly, have you seen a doctor to see what your projected final adult height will be? You could end up 6'3" by 22.
As for the nice guy thing, that I can't say. Though I do know that many guys who think they are "nice" are just dorks and geeks. Now I don't put "nerd" in there because I'd want to be a nerd...who doesn't want to be smart eh? Me? I'm a nice guy but I'm a buff bitch too

. I don't want to get all the ladies. So you have to ask yourself if you actually are the type who wants to get a l the ladies but just hasn't had the opportunity yet...which would make you not the nice guy.
As for getting on a diet for gaining weight, think fast food. But if you want to gain quality weight in the form of muscle, use a 1 gram of protein per lb of bodyweight ratio diet. Eat every 2 hours your waking period. Eat lots of eggs and tuna, they are economical sources of protein. And since you are skinny, don't be afraid to hit the whole egg, yolk included.
For supplements, you don't really need anything except multi-vitamins and maybe creatine. Creatine is like a muscle buffer. Stay away from fads unless you are rich, lol.
For training, remember the simple rule of more weight, less reps equals stronger but not larger muscles...moderate weight, moderate rep for ideal growth...etc. Guys get too macho in the gym with heavy weights and do nothing but develop bulk...no real muscle. Aim to look like Jean Claude VanDamme and not like Jim Belushi. Do 3 exercises per body part with 3-5 sets in a range of 10 reps, give or take 12. For example 12, 10, 8, 6...etc. Gauge what your body feels like it can do.
Eating normally but wiser, choosing better quality foods and training as above will earn you about 20-30 lbs of muscle your first year. Take it slow....
quote:
"Like I really only think about being with a girl to fall in love with her, unlike about 80% of the guys my age who just want some action."
I think you should increase that percentage by 10% and also remember that women are not all that different from men...so 80-90% of girls are girll jerks as well and just want some action...and money, lol. But learn to love yourself first, that'll enable you to walk a noble path alone and not feel lonely...making it all the more special when you do find those few females you wish to date.