Do not send that message to him. Again, you are trying to rush the process and you can't. Leave well enough alone and allow him to come to you. You do realize that you sound like you are putting pressure on him as well as pursuing him? If you are trying hard to honor his desire to have space and time....then give it to him. Texting, email or phoning him about that affair situation, retirement, etc., is not listening to him and what he wants or needs right now.
It is very normal for them to say that they are going to do something or come by and/or keep an appointment and then don't do it. Something else may have caught his attention or he went home to sleep. Whatever it is, it's just the norm for them and that's why you need to keep your expectations at zero at all times. The man you knew and loved is not the man you are dealing w/right now. You are dealing w/the mirror image of him, i.e., the opposite of the pre-crisis man.
I wouldn't have my SIL passing on messages to him. In fact, I wouldn't share one thing w/her. What is going is between you and your h. The more your SIL tries to get things fixed between you, the longer it is going to take. I know she means well, but she's not helping him or you at the moment. She's actually putting undue pressure on your h and he's not getting the time and space from her either. You may want to meet up w/your SIL and ask her to step back a little for now. She doesn't understand MLC or walkaways.
I wouldn't worry too much about what he said about "well talk when you get back". That may have been said at the spur of the moment and by the time you return, he may have forgotten about it. If he wanted to talk to you about something, he would have done it by now. So, file that comment away and focus on your trip.
Give him the space and time that he's asked for. If he texts you, then give it a couple of hours and then reply back. You do not want to sound like you are sitting on your phone waiting for him to contact you. I know you are anxious to know what is going through his mind, but you won't know until he's ready to tell you and that may not be for quite some time. If you and your SIL put pressure on him, he very well may say that he's had enough and walk away completely. I don't think that is what you want at this time.
Keep the focus on you and your trip. Dig deeper for patience and try to lower your expectations.
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.
