Why do I stop texting!?

I dunno why, but i'll be texting a girl and it'll go well and we'll maybe go out once or twice and then i'll say g-nyt one night and then not bother texting her in the morning or the next day.... and then obviously she thinks I don't like her so doens't bother tring to get in contact.

This happens to me quite a lot now and i'm only 19!, what can I do!? I don' want to seem needy and constantly text someone, but it would also be nice for somebody to text me if they haven't heard from me and just say "hey are you alright, are we still good?" or something?

Y'no... or am I wrong?