Friendships can hang in the balance when one friend starts doing more than the other. Friends with whom you always have to initiate contact and who never have time to hang out are hard to keep. You may feel that you're giving so much effort, only to get very little back. One-sided friendships make us wonder what happened to the buddies who used to always be available. You can take steps to deal with one-sided friendships, including telling your friend how you feel, sorting out your schedules, and in the worst case scenario, letting go.
Tell your friend how you feel about her never calling you or wanting to hang out anymore. Do not use an aggressive or confrontational tone. Let her know that you really care for her as a friend, and wish for the friendship to continue. If she truly values your friendship, she will take your words to heart and do what she can to make it 50/50 once again.
Work with your friend to come up with solutions to your one-sided relationship. There may be reasons why he has not called you in a while. Perhaps he just had a baby or got married. He might not be trying to avoid you, but has too many things going on. Offer a compromise, such as the two of you meeting up a set number of times per week or month. Work around each other's schedules to maximize your time together. Make up a schedule to keep track of when you two are going to hang out.
Let go of the friendship if all else has failed. While this will be hard to do, sometimes friends grow so far apart that they are no longer compatible. They develop their own lives, and it is up to them whether they want you in them or not. Cut off all forms of contact and move on. Do this only as a last resort, if your friend no longer seems interested in being around you.