I'm like you, while I know they are better somewhere else, I can't help but feel the loss of them. There truly is a strange emptiness in a home when one leaves us, even when there are many others still in the house. The space that they took up in the household was unique to them, and once they are gone one can't help but truly feel that something is simply missing. It eases with time, and I've simply learned to let the other rats and the next ones to fill their shoes pull me through it and help fill it in again.
It's a lovely way to think of your boys though, and I'm sure they are indeed surrounded by their share of eligible beauties now.