Her behaviour is abhorrent. I cannot believe the number of women who see no issue with the behaviour. It would seem many women only believe consent matters for women.
It is not rape, but in my view it is certainly akin to sexual assault and utterly nullifies consent. I am not sure the legal position but if it isn’t a crime of some sort, it should be. His consent was given to have sex using a condom as contraception, he may not have chosen to have sex if his wife had refused to use one, so he did not give consent to unprotected intercourse. Either consent for both parties is important, or it is not.
Deliberately sabotaging the condom is a huge betrayal- you should be able to trust your spouse when you have both agreed a form of contraception. Deliberately sabotaging the agreed form of contraception is sexual coercion by deception. In some cases (unlikely this one), there is also the risk of STI spread if the barrier aspect of the condom has been broken (even pinpricks do impact on it’s efficacy as a barrier to infection). It is simply not justified, under any circumstances.
And if this woman has done nothing wrong, and therefore, her husband should be absolutely ok with what happened, why not be honest and tell him? Why should OP keep it to herself and not tell her husband? The answer is that even those defending it know it is wrong.
The fact that condoms are not 100% effective does not mean one partner is justified in sabotaging them. Yes, if you chose to have sex using only condoms as contraception, then you do have to accept there is some risk of failure. But that is not what happened in this case, so it’s not really relevant.
If you are unhappy with your partner’s position on having children/the number of children they want and you cannot persuade them otherwise, then you either accept it or end the relationship and find someone who shares your goals. You should not seek to meet your own desires by sexually assaulting your spouse. Being angry at being strung along with regard to having children/more children is a relationship problem, it does not make sexually assaulting your partner because they won’t agree to what you want.
I could not remain friends with her after this. This is not the behaviour of a trustworthy person- if she is happy to deceive and betray her husband to suit herself, she’s capable of doing it to you too. I just could not accept it. And I wouldn’t lie to anyone for her either. You haven’t caused the relationship to end, her own actions would be responsible for the outcome, if the marriage were to end.