What would be your reaction?

WTF?

That would be my reaction!

It looks like you are married to my EX !!!
Thankfully, he is in my past now.
You can not live with deception forever.

I would be so miffed and a serious conversation would be in order. Immediately.

P O'd to the max. My ex wife did something like that, not a bike. I was pissed. We were suppose to of had an agreement that neither one would spend more than 100.00 without talking about it first. Other than bills of course. I kept up my end of that deal until she didn't. I had always said that it was our money. But I was the only one working. I never held that over her head but after that I sure wanted to.

I would silently plot his death. Well that, or I would buy whatever I have been wanting without consulting him. Whatever you do, don't get angry, get sad that he left you out and then hid it from you. He will feel worse then he would of if you had just yelled at him! You could also pretend that you have paid for something big that you actually NEED. He will be very uncomfortable keeping his splurge under the radar if he thinks that money will be tight for a while! You would have to say something like "well I figured it out and realized that we would just bearly have enough, but I am glad we got what we needed".

If you paid half of the money for the bike then it should have been in both your names and he wouldn't have been able to transfer the title without your signature.
I would be plenty pissed if I were you.

I would be ticked, and then demand 1/2 of whatever it sold for....it's only fair....it's marital property...you are entitled to half....

Then, I'd set some ground rules about future endeavors....Set him straight....

the word ****, amongst others, comes to mind