Dear Friend,
It was great to see you the other day and I really enjoyed our time together. I know you're really busy with work and everything else you have going on, but I hope you'll visit more often. I always have a great time when you're here and I really appreciate your company.
I know you're always welcome at my place and I hope you'll take me up on my offer to visit more often. I'll try to make more time for you too. I know how important it is to stay in touch and I value your friendship.
I hope to see you soon,
(writer's name)