In a time where all I see are baby pictures and engagement rings on my Facebook feed, I've begun to realize how I see my own life. Whenever I have thought about my future, it hasn't required anyone else still being in my life. While I have best friends and want to one day be in a relationship with someone, nothing about my future plans require other people being in it.
Let me clarify: you don't have to expect others to leave you to make plans that don't require others. However, it is important that your plans aren't reliant on other people. You shouldn't make future plans that will only work out if you are still friends with certain people, still have the same job, or are still with the same significant other.
Of course, I don't mean you can't make plans with people. You can go to concerts, plan dinners, even plan living together or having children together - but your long-term goals should be reliant on yourself only. If you have dependents, of course you can plan for them to be in your life - but that shouldn't fully distract you from end goals. For example, I plan on going to graduate school. That isn't because I want to impress others, because someone else wants me to, or because I feel like I have to. It is because I want to do it.
Similarly, if you have kids and you want to finish school, you should still plan to finish school. You can always figure out the circumstances as they go, but you shouldn't give up long term goals because of obstacles. Obstacles can always be overcome.
The best thing you can do for yourself is planning a life around yourself only. Whenever I make future plans, I make sure that it is what I want and not something that seems to be forced upon me. If something seems impossible, I make the effort to see it as possible. Goals shouldn't be limited or changed because others are no longer in your life.
If you want to have kids, have them - the person that you want to have children with may change throughout the course of your life, but that doesn't mean you shouldn't achieve what you want to achieve. Same with marriage - who you want to marry may change but that doesn't mean you shouldn't get married. Other things work the same way - grad school, travel plans, career goals, etc.
Ultimately, it's okay to be a little self-centered. Without being a little self-centered, set backs seem like the end of the road. But if you make plans for yourself, you tend to be less worried about how other people will affect you and no longer have to be tied to something that might not be good for you.