Inability to communicate is very deep rooted and races back to one's childhood, their upbringing and their experiences, which cant be changed. The only thing that can help you overcome this problem however, is your will to make this relationship work. If you're truly interested in making it work you need to take the first step, as I m sure in a 5 year long relationship the guy must have done it many a times. You have to first make him understand your inability and at the same time also assure him of your intentions to try and overcome it. Start by writing if that suits you..take it to telephonic conversations and gradually to face to face communication. If he is also genuinely interested in making the relationship work, he might be glad to help u overcome it, but he needs to see the efforts from you first. No matter how deep the love, affection and understanding, please remember absence of communication poisons it all.
Go save yours before its too late. All the best!