Hi Rosenicola, I hope all goes well for you and your BC. I have a male Collie, 3 in October. Although never snappy with me, my partner, family and friends, he can NEVER be around children, with their unpredictable movements and loud noises!
He is a lovely dog, but they do need a lot of stimulation. I must admit, he doesn't get as much stimulation as he should, but we try our best. It is VERY noticeable, if I leave his big walk until later in the day, tht he needs to get out-he's like a tightly-coiled spring! He is oddly food possessive, although he has never had to be, if that makes sense. Before castration, he could be quick to react to other male dogs, although he wasn't a "h*rny" dog, he didn't hump, or chase after the ladies! However, castration calmed his response, and I know he won't ever get any cancers etc. "down there". The op is relatively quick, they took Jack in early in the morning, and he was ready for pick-up by 2pm.
I understand you may be feeling a little shaken or upset-it's natural, especially when your dog obv. means so much to you. Don't let his actions hurt you though, first and foremost you are his owner, and you'll have to remain a little detached in order to see the problem rationally from outside. The advice here is usually very good, so you're right to come and ask everyone. There's some v knowledgable people about :)
Let us all know what the vet says, and how he is. Give him a pet from me.