How great is it that you have someone in this world who has the ability to make you happy, excited, or even sad. How lucky are you that someone means so much to you that you are able to feel so deeply as to what their opinion of you means. Some may think it's a bad thing to let someone affect your emotions, but I think it means you're human. Emotions are the best gift that we were given. Isn't it amazing that our body literally cannot contain the amount of joy we are feeling, so we laugh. Or that we could be so hurt that tears run down our face.
Yeah, being sad isn't fun and at the time you want that feeling to go away (which it will) but just imagine what your life would be like if you couldn't feel sad? or you didn't have the ability to feel the amazing feeling of pure happiness. I would rather deal with the pain of hurting for a while than to have the option of never having to feel it again because it makes you a real person. It shows you what your morals are. These emotions help you figure out how you want to live your life. We feel emotions that we may not even realize. And sometimes you may never really know what's going on in that complicated mind of yours, but your body will literally force you to figure it out.
Also, the best thing about these emotions is they show you who really should be in your life. The more the actions of someone else affects you, shows how much they mean to you. All these emotions that you hate feeling like guilt, jealousy, hatred, grief, resent, these help you and they lead to great things such as being happy. Be thankful you have the ability to feel so much and so powerfully and be thankful that you have people in your life that can cause pure joy. Because one day if you woke up without these feelings, you'd want them back.