That phase in life when you let someone in, with your hopes high, like way high, it's all laughs and everything nice, you share past memories with them and let them in on a lot of stuff because of the happiness and comfort you feel when In their company.
This is perfectly reciprocated in most cases that I know of, both parties feel the attraction and connection, occasionally, sacrifices are made in order to make the other happy or at ease in a difficult phase of their lives.
Albeit, the story line never maintains this beautiful perception in most cases. A period comes, one feels too occupied with schedules, the other feels left alone. Regular conversations become rushed ones or periodic talks, the communication dims.
One finally stops trying, deepening the silence, the silence feels piercing to the other, and finally gives in to the new trend as well, a perfectly blossoming relationship halts abruptly, in most cases, both parties still wonder why and how.
The root problem is communication, the inability of one party to explain to the other what he/she feels properly. Even when misinterpretations cause the drift, communication is still key. Even at the set in of the piercing silence, communication still helps, unless one party is too pained to speak or feels words wouldn't explain.