You can put boundaries on your-self. You have noticed a pattern in your-self. Meet guy, he says sweet things to you, then X. X is typically a projection in the future. "This guy could be the one." Or some other "romantic" Walt Disney like idealism of a relationship. Learn how to watch your thoughts and recognize the patterns you fall into. And then redirect those thoughts to what will serve you better.

At least for me, this is where I would get "attached". I would attach my-self to an idea. My mind would think something along the lines of; "Finally, someone who gets me." Or some other bs I would tell my-self. Again! Learn to watch your mind do this to your-self! When we "attach" ourselves to certain "expectations" or ideas it typically leads to disappointment.

The key here is to take ownership of your feelings. He did not do this to you. He did not MAKE you feel this way. You did it to your-self! Simply put, pay attention to your patterns. Once recognized, practice, letting go of the idea you are attaching yourself to.