Don’t make your definition of friendship, whether or not someone will leave their other friends to talk to you. Or even whether that person invites you. Some of my best friends don’t invite me much and vice versa. What matters is the connection you feel with that person.
If they are in a room go join them. Don’t invite them and expect them to leave their other friends. That’s the definition of the opposite of a friend. Your wife or lover might do that but not a “friend”. And anyone that puts requirements on being their friend clearly isn’t a friend anyway. Threatening to leave or unfriend someone for not spending enough time with you means you’re the one not being a friend. It’s ok to unfriend acquaintances. But if you’re doing it to be vindictive, then you’re the one that’s not being a friend. We all lose track of even some good people. There are only so many hours in a day and there are way more good people here than there’s time to see.
Here are some good tips for building a friendship: If you really want to see someone that you’re not able to get time with, look for clues to who their friends are and try to make friends with them. Also search for their rooms and add them, or add any room you see them in to your favorite rooms. Never pressure someone in here to do anything, because they can just click away and pressure may back fire. Make them WANT to do it. Send them a nice roleplaying note with a gift that shows you shopped for something appropriate. Ask for a favor or for their opinion or tell them something small but kind of personal.