You need credit that offers 0% interest loans if paid back in 12 months next time this happens. Many appliance and furniture stores finance this way. Ask them, if there’s a next time.
Your boyfriend also needs to work as hard to pay for things. If he makes more than you, he can contribute more accordingly.
My vote is don’t owe your in-laws, unless it is because you will be in danger of losing food or shelter. It could affect how they view you, even unintentionally. You did great paying her back, but you want her to see you as the adult you are.