I'd recommend spending as much time with him as possible. I had the same sort of dilemma at the end of my first summer working at the camp I volunteer at. I had basically found my heart horse (he still is my heart horse, there's no way around that) and the hardest thing I've ever had to do was watch him be loaded up on that trailer at the end of the summer. In the weeks before the end of camp I basically spent every moment with him, just loving on him and I even walked him on to the trailer myself when he had to leave.
Sure, I bawled like a little kid off and on for the next week or so but in the end I know I did the right thing because he knew for sure that I love him. I still get teary eyed every once in a while thinking about him but it's made easier by the other special horses in my life.
It's one of those things where you will never love a horse for the same reasons that you love Junior for but if you give it a chance you'll find another horse that needs you just as much as Junior did/does and you will adore that horse in a different way.
For instance: my first horse love, I loved him for the freedom he gave me over jumps and the confidence I gained from working through his issues with him. We had a deep connection that no one could deny and it was very hard to let him go.
My second horse love, I loved him for the trust he put in me, even when I could barely trust myself, and for how he made me feel like I was the only person in the world that was worth anything. If I was in the barn he would ignore everyone in an attempt to get my attention. He gave me his all and I walked him on to the trailer to send him home, yet he still loves me. He was back at camp last summer and he was having some issues that I came and fixed and he let me right back into his heart even after I kinda let him down. And yes, writing this has made me tear up.
Lacey is still worming her way into my heart but she's teaching me that I need to trust her and let myself go. I love her for the way she's teaching me to trust and I love her for how much she needs me even when I think I'm worthless.
Each one has been very important to my journey and I love/d them all very deeply and dearly, just in different ways. I hope you will continue with horses because you will find one that needs you just as much as Junior does/did and you will grow to love that one too.
And sorry for how long this is. >.<
Fabio - 13 year old Arab/QH gelding
Hazel - 14 year old Angora goat
Atticus - 4 year old LaMancha/Alpine cross goat
Rest peacefully, Lacey.