Pity Friendships

Does everyone have that one friend who they still talk to just because they've known each other forever? I have one friend whom I've known my entire life, but as the years have gone by, we really don't have anything in common anymore. We're at different stages in our lives, we have different interests...We wouldn't be friends if we had just met. But the past keeps us together, and obligates us to stay in touch. Well, obligates me to stay in touch. I believe my friend thinks we have a good friendship, and I assume she enjoys spending time together and talking with me (since she's always the one who initiates things). But the friendship certainly does more for her than for me. Talking on the phone with her or meeting her for lunch is like a chore more than anything else: something I need to check off my to-do list, but not something I look forward to. It's just the she does all the talking, I don't get a word in edgewise, and we talk about the same things every time anyway: her school, her family, her future. She'll ask me, "So how have you been?" out of politeness, but as soon as I say, "Fine" the conversation immediately turns back to her. If any other friend treated me this way, I'd simply cut him or her out of my life. My mantra for friends is, "If you don't make me feel like a f***ing ray of sunshine every time we're together, then I don't want to be friends with you." But I feel like she needs me. I'm her one normal friend who's moving forward in life; I bring stability to this friendship rather than chaos or dysfunction. I want to be there for her when she needs someone to talk to, but it's an unequal friendship. It's not like she's the person I go to when I need a shoulder to cry on or when I want to talk about a great date. I assume we will continue get together every couple of weeks out of the routine we've created, but I do wonder if I'm going to be in this "pity friendship" forever...