I think it's fine for a couple to decide to pay exactly their own way - and to be paid back for loans. Not a popularity view on here, but I've had a relationship like that perfectly successfully. In the past - but the split wasn't money related.
Of course, I'm not talking about a couple where someone has made career sacrifices for the other, child related or not. And there's a massive caveat about how bills are split.
What's missing here, is the OP hasn't even said if she wants to go on the more expensive holiday.
If you can afford Spain but you'd both love diving in the Maldives and that can happen with his loan and you know you can pay it back after 3 months - meh, your business.
If you both want Spain pool and beach but he wants 5 and à la carte but you can only afford 3 and AI - then he can suck it up.
My XH and I earned the same - I wanted a weekend in my camper van, he wanted 5* hotels. It wasn't about money, it was about having totally different tastes. I resented the times I spent £150 a night on a hotel but didn't enjoy it as much as I would have a £15 campsite.
I'm now about 4x the highest earner. We just came back from the US (a child each too). We chose a holiday we both really really wanted. We booked flights and accommodation that we could both afford. We self catered a lot because we like to, AND to save money - because we like to, not need to. Then I paid for every extra - meals out, the food shopping for self catering, activities, museum entries... it works for us.