Yea, this happens with literally every single person on the planet at some point or another. As you grow into yourself, you tend to grow in whatever direction that will lead you, with most, it tends to grow apart, with few it grows along, but it isn't something to take to heart. If anything it's an opportunity to meet new people, and guess what? The SAME thing will happen with them one day too. But your question is on how to make new friends. A few of these people recommended goin to organizations or whatever that suits your interests and they're exactly right. I mean, you don't HAVE to join anything, but if you know you like doin something (Music, gaming, cars, whatever) go somewhere that you know those people tend to frequent, or even events that are themed or created for those interests, you're guaranteed to meet some people, provided that you're willing to talk to strangers.
That's another aspect of it. You can't meet new people if you don't....MEET new people. Don't be anxious, don't stress, just throw yourself out there, say somethin silly, break the ice, just be yourself like you were with your other friends, if anything look at them as if you're ALREADY friends, and the conversation will flow. Next thing you know, you'll meet their friends, or other people, and the connections will continue building.
It's all good man, this is only a short portion of time you'll deal with this, just get out there and make it a goal to meet people. You'll thank yourself later.