Portia, Don't beat yourself up. The words "I miss you" can mean any number of things. It could mean you miss him chatting/texting w/you, it could mean you miss his warm body close to yours or it could be that you just miss knowing he's out there. It's all in the interpretation and it's nothing to worry about.
I wasn't expecting him to respond back. It took a lot of effort on his part to even send you a card or wish you a happy birthday. He's on Pluto and you got a postcard from there. Now, it's time to get back to focusing on Portia and what is Portia planning for spring this year?
Hang in there. You did nothing wrong.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.