How do I be a less Needy Person?

I am an extremely needy person. I always need someone to talk to or text. and when texting, i always need the person to reply quick. I can't stand sarcasm because it makes me insecure of whether or not the person means it. Also, I've been texting this girl and i really enjoy texting her. i have no plans to get into a relationship with her and neither does she but we both enjoy each other's company. But now, she's away for about a week, i even though i've grown very reliant of her company these past months, i really need to stop feeling this way and start relying on myself. I mean, i can't be needy forever right? and i take this week as the good as any to start on my path to inner security of myself and feeling more confident and less lonely when alone. And, don't ask why, but as of now, i don't have much friends and i don't have anyone i can confide in other than her. I've been really depressed/confused this past year and this has resulted in many wrongdoings in my life. I have to stop being needy and dependent but i realize that I need help doing that. Hence, does anybody have any good advise that can help guide me onwards to my destination?