Maybe he was using it to have a wank without making a mess?

He probably just wanted to make a great water balloon. If you want to cause a ruckus, splatter people with a warm mayonnaise balloon.

NGL I once wanted to see how far I could stretch a condom before it split.....

I don't know how trust worthy your boyfriend is so I'm not gonna say for sure he's not a liar, but to be fair it is REALLY fun to stretch your hand around inside a condom.

Unless you have reason not to, I world believe him. They're fun to play with. My husband blew one up like a balloon and played with it for a whole day.

Did you ask him exactly where he was going to put that hand?

He could have tried putting it over his head and use his nose to blow it up like rubber gloves. It is a blast thing that guys do. We are stupid like that.

Like others have stated, unless you think there is truly a chance or a reason he was cheating, I’d believe him. This is something I can absolutely see my husband doing, and you know what, I can see myself seeing this too. Condoms for non-sexy purposes can be a lot of fun, they’re waaay better than just about any regular water balloon! If there really is reason for suspicions, I’m sorry you’re going through this, OP. I really hope it isn’t the case!

that's even worse than when I found a condom wrapper and he blamed the rabbit

Every guy has done that.