If your boyfriend's love wasn't sincere, isn't it better for you to find it out now than later on? I know this is a deep emotional blow right now, but in time I suspect you'll actually be thankful for it.
I know it's hard to untangle your emotions at a time like this, but I want you to understand two very important things. First, why are you feeling so devastated? The real reason isn't simply because you've lost your boyfriend; instead, you feel rejected and betrayed, and you may even be wondering if there is something wrong with you or if you aren't worthy of being loved.
But this isn't true! God made you, and you are a unique and important person in His sight. In fact, you are so valuable to Him that He was willing to send His only Son into the world to give His life for you. Don't let feelings of rejection or worthlessness overpower you, because they simply aren't true.
The second truth I want you to know is this: God loves you, and He has a perfect plan for your future. Turn to Jesus Christ and ask Him into your life today. Then commit your future including your relationships to Him and ask Him to guide you. The Bible's words are true: "If God is for us, who can be against us? He who did not spare His own Son, but gave Him up for us all how will He not also, along with Him, graciously give us all things?" (Romans 8:31-32).