"You must choose between your happiness and attachments." -Adyashanti
One of my favorite books is, It's Easier Than You Think-The Buddhist Way to Happiness, by Sylvia Boorstein. She talks about the "Noble Truths" one of them being, attachment. When you attach yourself to someone, something, some idea or some outcome; you set yourself up for fear and anxiety.
What happens is your fears begin to well up thinking you may lose this person, this thing, this feeling or you are afraid you may not get what you want in the end. And, we all know that sometimes things work out the way we want and sometimes they don't. But it is in being attached to the outcome that we suffer.
Instead, try enjoying the journey. If you are with someone, revel in that person and how they may enrich your life instead of worrying about if they will leave you or not love you. If it's some thing that you now possess that you've been wanting, be grateful and enjoy it instead of taking it for granted or wondering if it's too good to be true.
If it's some particular outcome you are wanting, don't get caught up in "what if" since everything always works out in the end anyway and this too shall pass. Acceptance of what is and appreciating what is right now allow you to embrace the moment and simply enjoy. Whereas, wanting to control the outcome, the person or whatever it is you desire, creates feelings of vulnerability, fear, and anxiety and then causes you unhappiness.
Learning to allow things to happen as they will and learning to have gratitude for each experience brings with it an inner peace and faith that no matter what happens; it's all good. Life is a series of lessons and it's working to help you find a better understanding of life and to help you realize that happiness doesn't come from something or someone outside of us.
Don't let external things have the power to make you miserable. Release the feelings of being attached to anything or anyone and find the peace within that is your real happiness. We are not separate from goodness, it is with us always; it is attached to you so to speak! So if you are going to attach yourself to anything, attach yourself to the happiness within you.