For the sake of your own self-esteem, do not chase others. I don’t mean to just wait around and never take the initiative to get in touch with people and organise outings, but you should not have to persistently chase someone to get them to stay in your life. If you’re always the one doing the chasing, something is wrong.
It might be that you’re scared about not chasing them because then they might leave your life completely. I know it’s hard to accept this, but if this is the case, they are not worth your time. Anyone who is worth being in your life should make the effort to be involved in it.
So either give them a nudge and tell them you’re not happy doing all the work, or even better, get on with your life, with the people who make an effort and deserve your time. The person you’re chasing will either realise they need to change their ways and end up appreciating having you around much more, or they will leave. If it’s the latter, at least you know now.
Just do your thing and it will attract the right people.