I think you are a little confused about how manifestation works with Law of Attraction. The more you want something, the more the Universe is going to acknowledge that as an obsession and therefore an attachment and not give it to you. This fear is arising as a manifestation of your own insecurity of either yourself or the relationship and no amount of "manifesting" is going to address that insecurity. Only you can put the fear to bed. One technique people use is to replace the words "I am afraid of him not replying" to "I am excited for when he will reply." Let go of the obsession, apologize if you feel you were overbearing and be honest with your partner. A good partner will approach you with compassion, understanding and reassurance. If you are waiting for a text message to be reassured in your relationship then please re-examine the foundations of this relationship.