“Dear Jasmin,
How come I always get excited about a potential relationship and then it doesn’t go anywhere?
-Frustrated”
That is definitely very frustrating, and not a fun habit to be in. As humans, we long for companionship, and often feel lonely and frustrated when we don’t have a significant partner. More often than not, these difficult feelings can lead to a bit of neediness. When approaching a new potential mate from a place of feeling a bit needy, it is easier to give him or her an “A” before they have actually earned it, which ultimately sets you up for this reoccurring disappointment.  It is important to approach dating with the knowledge that most potential mates will not be your perfect “grade A” fit (if it was that easy you would already of found him or her!)
When we create fantasies around how great this new person is, and daydream about the future together, before getting a chance to really know that person, it is usually inevitable that their grade starts dropping because they hadn’t actually earned it yet. (related article How to Find and Keep a Great Relationship)
As much as we love the idea of “falling in love” and the experience of the butterflies and excitement that comes with a new relationship, it takes much more time and depth to create something that is everlasting. This is why I recommend to approach new potential partners with openness and willingness to connect, yet with enough sense of reality that we don’t give away the “A” before he or she earns it. If they are good enough to make the grade, they will; just give it time.  Focus on who they truly are rather than who you hope they will be.

Hope this helps!