There are activities and associations that being in a relationship naturally move us away from as we mature together. For example, committed partners aren't going clubbing with all their old single friends. That's not to say you drop those friends. But, the things you do together must shift away from the old opportunity creating activities, like clubbing to be with singles and meet other singles.

That doesn't mean dumping your single friends. You just have to choose activities together which don't put you in the way of single life behaviors. If a partner will not make that change, why be in the relationship?