I want to say "Don't marry her", but if you don't, you won't have those 2 really wonderful kids. You decide(ed).

 Don't make your whole life about him. You have much more to live for than a guy.

 She will always be the favourite - Daddy's girl, the popular one, the beautiful one. You're the studious, adventurous, courageous, independent one. You always wanted to be her. She'll never tell you, but she wishes she were more like you.

 It'll be the most awkward kiss of your life, but it she turns out to be the best girlfriend ever :)

 Your illness is actually a blessing in disguise. Don't lose hope.

 Don't let fear and rejection keep you from trying. You're going to fuck up every once in a while but, at least you can say you tried

 Get out of that unhealthy relationship. If he hits you he doesn't love you. Don't let him force you into doing anything your uncomfortable with. Please, fight with all of your might. It may just save you a ton of issues in the long run.

 Stop playing videogames, stop reading books. The things you need to learn and to do in your life depends on how well you interact with others. Go outside.