I am so sorry you had to let your Little Man go..and not that long ago. I am glad to read you do have your 18 year old kitty. It is nice to have a furbaby to hug...especially at times like this when you feel so low.
You certainly did not let him down in any way. As hard as it is...when we put their distress before our own...that can never be thought of as letting them down.
Maybe you had the feeling of wanting to do more. That I learned a long time ago...is a thought I let go of rather quickly. I have just come to accept the belief that when it is their time to leave us...there is nothing and I mean..nothing..we can do to stop it...all control and ability to help is taken away from us....else it would have happened. In fact, the only "help" left to us is making the final decision which is a decision we make FOR THEM...never for us. The babies who are "lucky" have the type of human who WILL help them when they need it.
You are one of those people and your boy knew you would take care of him as best you could and if the time came..he had to depend on you for that final decision to give him peace.....again...he knew you would take of it for him.
So yes let go of any negative feeling about making the decision. In fact, I guess we who have had to do that ..in a way...are glad we were given the time to arrange that rather than witness the inevitable conscious ending. I am so glad I was home when my Little Guy was in distress and we were able to give him peace..even though I never expected to lose him that day. I am thankful because if we were not home when his problem happened.....he would have suffocated to death...alone. So I can be "thankful" I was there to "help" him when he struggled for help.
So your ideas of remembering the good memories you shared with your Little Man is the right idea and I encourage you to do that as much as possible.
Just remember WHY you made the decision then try to push it out of your mind by deliberately thinking of when he was healthy and happy to feel good and all the little things he did that made him so precious to you.
You also said you feel no one can understand your pain. People here do understand your pain because it is the exact same pain they have, have gotten through, or have been there and know they are going again soon. The cir%%stances may not be identical but believe me, the pain is just as intense, as devastating, as horrible as what you are going through. What helps is KNOWING you are not alone in your pain. We all share that same pain. We grieve in our own way and many grieve similar..many grieve differently but having your heart ripped out...feeling the loneliness...the emptiness....that's all the same. That's why people here are talking to you from the heart....because they do understand. Everytime we read someone is going through what you are, we type through tears because our own pain rises again as we remember how we felt and still do...when we allow the pain to come back.
Each one of these babies is special and unique in their own way and only they and their human friends have their special bond..but we all have the special bond of loving them and being loved by them....we all have felt that...we all miss that...we all know that no matter how many enter our lives in the future...there is one place in our hearts for each one we have lost that is theirs and theirs alone....forever.
It may help to post pictures of your Little Man, to tell stories that make you smile at the memory, to write him a special note here with your thoughts and feelings...anything you think of that makes you feel better..even for a moment..is the thing to do.
Give your 18 year old old-timer....lots of extra hugs and kisses and let him know he is special....that even though you are hurting terribly inside.....that being able to hug that furbaby means something extra special....especially at this time.
One Mom here said a long time ago: The pain of losing him will never ever be greater than the joy of knowing him.
That is a strong thought to keep in mind to help push down that pain that will never leave completely but can be lessened
over time.
Hugs to you and your old baby and to your new Angel.....your Little Man