The hardest part of parenting, so far

It's been busy since we got back from vacation. It's not been that I haven't had anything to say, just a lack of time to really put thoughts together in a cohesive way. I also think that maybe I was trying not to think too much. Getting Corwin ready to go to school became a series of things to do, a way of being busy enough not to deal with the reality of him leaving.
I really don't know why this has been so hard for me. But the bottom line here, is that it has been and still is.
As we were getting ready to say goodbye this weekend, there came a time when I was almost overwhelmed with the urge to punch my son in the arm. Now, I am NOT a violent person, so this was really one of those "out of nowhere" feelings. I realized that there was this part of me that was angry at him for being so smart and getting into a good school that took him away from us for the next 5 years (dual major in engineering and physics - it takes an extra year). That was bizarre enough to almost make me laugh. And no, I did not hit him :)
My biggest dilema was how to tell a son who is uncomfortable with displays of emotion how much I love him and not only love, but like! I really like the young man my son has become. He has an air of confidence without arrogance, he is funny in a quiet way that sneaks up on you and leaves you laughing even hours later. He is strong and tender hearted, smart and frugal and compassionate. Sure he has his faults but all in all he is a great son and I am proud of him beyond belief! And I couldn't tell him any of this to his face. I would have cried and not been able to speak and then he would have been embarrassed and I would have felt bad for embarrassing him and it would have been a mess.
When it was time to leave, I needed to leave. The rest of the family took their good sweet time saying goodbye and it just about killed me standing there and not crying. This is truly the hardest thing I have been through as a parent. Saying goodbye to Amber, when she went to Master's Commission, was not this difficult. There was never a question in my mind or heart about our relationship. I knew she would be calling every day and she was only 2 and a half hours away. I missed her terribly, kept having to remind myself that she was not around, but it didn't hurt so much.
I am still trying to figure this out. I don't know if it is because Corwin is my only son, or simply a son, or if I have a different relationship with him than some moms or what. I don't love him any more than my girls.... I love them all with all my heart... how can you have more or less that all? But I miss him!!!! and it hurts.
At the risk of over spiritualizing this, it has gone through my mind many times over the last couple of weeks - how God must have felt sending His only son to this world, knowing what was going to happen to him, knowing what Jesus was going to go through. That must have been awful! There is comfort in knowing that, certainly, God understands what is going on in my heart, and a bit of amazement and guilt that I should be struggling at all, when I consider that Corwin is only a phone call away or 6 hours without traffic. It is not like I have lost a child or sent him off to war. It is college, for heaven's sake! But I miss him and it hurts.
A friend of mine, who has been through this 3 times, keeps telling me that it gets better.... not just that the pain goes away, but that the actual relationship gets better. That there is a transition from parent-child to friend and it only happens through the separation process. I am clinging to that thought! I am choosing to believe this. So there it is.
It all comes back to this one thing: Faith. Do I trust God with my son? Yes, of course. He is God and He gave me Corwin in the first place. I am only his caretaker. Corwin is on loan to me. I get that. Do I trust God with my heartache? Yes. He has proven to me over and over again that He will see me through anything. And I KNOW that He will see me through this too! But it still hurts and I miss my son.