Please, don't be angry with me. Recently I've been busy all the time, and I haven't had the time to talk, but I want you to know that I really like to talk with you and, whenever possible, I'd like to have a contact with you. You seem to be very nice.
See you later, I hope.
That's a pity that you're not available(szkoda,że jesteś niedostępny)/ not here (dosłownie, że cię nie ma)
lub I wish you were here now. ( Żałuję ,że cię tu teraz nie ma)
Regards (pozdrowienia) lub Take care (trzymaj się)