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bluelonelyheart Boiling water sterilises things just fine.
Maybe come to a compromise, is it so bad if he does buy one?
We may not always agree, but it's obviously not something worth feeling such friction about. If he wants to pay for it then let him, It's not about winning the argument when there's no real "loser" at the end of it.
About the part with him blaming you in the future, this is fictional so far. Why would he say something like this?.
If you let him do this then you show your trust and he couldn't say such a thing as you've let him do this.
Weigh up the pros and cons of this with a clear head and you'll find it funny about how little this really matters.