There will always be people in this world that want to stand in the way of your dreams. Whether it be a teacher, a family member, an old friend, or even just a stranger. As hard as it is to grasp, not everyone has your best interest in mind. Human beings can be selfish creatures, and might even turn things around on you. You could put yourself out to help them, drop everything in a blink of an eye. You could open up your heart and home just to have them betray you when it seems most convenient to them.
These people will say they are the ones who have been wronged. Most likely they will believe it too. They will play off of peoples' sympathies in order to make you seem like the bad guy. Let people believe what they want to believe. Years of established "friendship" is no reason to let someone walk all over you, and certainly no reason to feel coerced into feeling that your emotions are invalid. They're not, feel anything and everything you want.
There are days where you'll feel like you cannot succeed. There will be plenty people around to confirm that. They'll word this somewhere under the lines of "looking out for your future," and "keeping your dreams a part of reality." Know that you are going to surpass even your own expectations, and even the most "sound" advice can be wrong.
Whatever you do, don't let a few rotten apples ruin fruit for you. Never judge someone by their first impression, because even the most putrid apple can have a delicious candy coating. Don't be afraid to branch out and meet new people, because even the pointiest pineapple can be sweeter than you imagined. Keep your head high, your smile bright, and your dreams in eyesight.