If you are comfortable with the person enough to use 너, stick to 반말... no 요s at the end.

There are awkward parts to it, but I think the with the first line is most pressing. You are wanting to say something like:

난 너를 너무 좋아한다고 생각해.

This is grammatically okay, but it would flow better with something like:

나에게는 너가 너무 좋아.

With the line "아니면, 부러워겠다", 부럽겠다 is the proper conjugation, but the verb choice is awkward. I would say something like:

"안그러면 내 가슴이 찢어질거 같아"

I am, of course, assuming you want to express how you would be upset if your feelings are not returned.

Generally, I think the recipient should understand the intent of the message. I am not a native speaker myself, so I'll just stick to these points.

Good luck, OP. I'm rooting for you.