Close friendships sometimes follow a similar pattern to romantic relationships. Two people realize they have a lot in common. They get closer and closer as they share experiences and help each other through tough times. Then something happens and they no longer feel like they can understand each other. Eventually they drift apart. You may not be able to keep your friendship from changing, but the key to preserving it is to change with it.
Trouble on the Horizon
If you feel like your best friend is drifting apart from you, you're probably right. Unless you're prone to anxiety about all your relationships, a gut feeling that something is changing is most likely reliable. Your friend may be calling less often, not returning your calls reliably or canceling plans with you. You might have noticed a tense feeling in your interactions lately, or your lives might have changed so much that you have less in common than you used to. Before you set out to save this friendship, you should ask yourself if that's really what you want.
As much as you might be attached to the idea of staying best friends forever, the reality is that people are constantly changing because life is constantly changing. Two friends who did everything together in college may have very little to say to each other twenty years later when they live on opposite sides of the country and have different careers and different family situations. That doesn't mean they don't care about each other, just that there may be no basis for an ongoing relationship. If you truly feel that your friendship has what it takes to last, you'll need to find a way to adapt to the inevitable changes of life.
Adapt to the Situation
Sometimes people become distant because of circumstances more than choice. For instance, if you're single and have a lot of free time while your friend is married with young children, it would be unrealistic to expect your friend to have as much free time to spend with you as in the past. Rather than trying to hold on to the way things used to be, you can keep your friendship alive and relevant by accepting that things have changed and adapting accordingly. Instead of asking your friend to come out for coffee, you could offer to come over and help with childcare while you catch up. Whatever the situation may be, you'll do better by adapting to it instead of fighting it.
If you haven't been in touch with your friend for a while, you can reach out by sending a message or calling. Keep it light and easygoing -- you don't want your friend to feel pressured. If you make the first gesture and show that you're available, it will be easier for your friend to reciprocate and make plans to get together. You may find that you have the type of friendship that can pick up right where it left off no matter how much time has passed.