Most Helpful Guy
Why? because you are both forming connections that are based on the mind and the ego, rather than the soul and the higher self. At first, the ego is satisfied with it's new food, it feeds, all of the dopamine and other feel good chemicals are increasing by the day and you spend all of your time together... it feels like love... like you are soul mates.
But due to this being a mind / ego based connection, eventually the ego tires because it can never be satisfied, it wants more, so it begins to check out and look for something new. Your bfs ego wants to feed on something new, and your ego wants to continue feeding on something 'old'. Rinse and repeat...
This is why we have the hookup age, and it's why dating sucks for most. To add to this is the important levels of consciousness. Most people are operating through a lower state of consciousness or the 'lower' self. With this level of consciousness, true love is impossible, and your relationships will always end because they never really began in the first place.
To have more fulfilling relationships, you need to work on your self, your state of consciousness, discernment, you need to learn how to 'silence' your incessant internal chatter box, and you need to be able to bring others into a higher state of consciousness, or know when they cannot be helped.
All of this can take a lot of work, and can be a lifetime transmutation. All of your relationship problems are internal, and all of your partners are operating at a 'lower' state of consciousness. There are also elements of emotional unavailability as well.
If you feel ready to change your life, and way of 'thinking', seek out the book 'Power of now' by Ekhart Tolle. That book taught me how to silence my mind so that internal narrator is gone when I want it to be. This brings you into a new level of peace, and if you are in a relationship, it will have a huge impact because you can no longer become angry among other things. If the book appears to be a load of nonsense, it just means you are not ready yet...