[CHANGING] IN EVERY POSSIBLE WAY= Changing completely, in every thing.

IT'S NEVER QUITE AS IT SEEMS= It's different from my perception (reality is always different from appearances). The word NEVER is more emphatic than the normal negative NOT. The preposition AS here is a comparative.
The word QUITE there is very British. British people often overuse this word to the point that it really means nothing. It usually means RATHER, but not here. In this case it means EXACTLY.

I'VE FELT LIKE THIS= I have felt this way. In British English we use the present perfect tense (have + past participle) when we are talking about life experience and we don't say exactly when it happened:
- I've been to Paris twice  (life experience, date is not important)
- I went to Paris in 1987   (past experience located in time)
- I've studied French
- I studied French at school
In American English the present perfect is much less used than in BrE, so they would most probably say here: "I never felt like this" or "I never felt this way before".

I'M FEELING IT: it = this feeling

BECAUSE IT CAME FROM YOU: it = this feeling

I OPEN UP= I become aware. If you have a wrong perception and then you open up, you suddenly realise you were mistaken and see things as they are.
Other common uses: If you "open up your mind", you accept a different way of thinking and put aside the conventions and prejudices that stopped you from seeing reality more clearly. If you open up a door, you open it wide. If you open up, you start speaking without inhibitions (e.g: Yesterday she opened up to me and told me about all the problems she has with her husband).

THE PERSON FALLING HERE IS ME= The person falling in love in this relationship is me, not you, so you are not in love with me.
- To fall in love (sometimes simply "to fall") is to become desperately in love with a person, to love them so intensely that you want to be together all the time. You can say "I'm falling for you" or "I'm falling in love with you".
- To be in love with a person is usually deeper but less intense (and more real and solid).
- To have a crush on a person is similar to falling in love, but more sudden, intense and most of the times temporary (the kind of love more usual when you are a teenager). The person who has a crush usually thinks they're in love, because when you have a crush on someone it's difficult to realize it's only a crush, it feels too intense to think it's just a crazy, groundless and temporary situation.
- To love someone is the general feeling, not simply in a romantic relationship like the three expressions above.

THEY'LL COME TRUE= The dreams will become real.
If something comes true, it becomes reality.

IMPOSSIBLE NOT TO DO= It's impossible that my dreams won't become real (because I wish it with all my heart).

I TELL YOU OPENLY= I'm telling you with no inhibitions, even if it's hard for me to say.

YOU HAVE MY HEART= I love you so much.

YOU'RE WHAT I COULDN'T FIND= You are the person I always wanted to meet but I could never find... until now.

TOTALLY= This word is used to emphasize and it has a stronger emphasis than "very" and even more than "really". (e.g: You're totally awesome = You're absolutely amazing = You're really really fantastic)

AMAZING= Wonderful, fantastic, incredible.

SO UNDERSTANDING= We can use SO to emphasize an adjective or adverb in a similar way to "really" but more intense. It's like the –isimo ending in Spanish or Italian (la donna e bellissima = the lady is so beautiful  /  esto es grandísimo = this is so big / this is really, really big)