I love languages as well, I took French and Spanish for GCSE and actually finished my French GCSE yesterday (going to miss it ngl). A few people I know who took double language at GCSE did not like it, but personally I loved it and wouldn't have taken anything else. Languages always went well for me all the way from year 7, even though I only started French and Spanish then, and I was probably one of the only people in my class who loved it so much. I grew up bilingual so they do come to me a bit easier, and I'll be honest I didn't put that much work in, I just always tried my hardest in lessons because I think languages aren't something you can just cram the night before the exam, you have to pick them up over a long period of time. So, other than putting in my full effort with lessons and homework, I haven't revised loads for my language exams (apart from speaking, I did quite a bit for that), but I found French fine and I'm hoping for 9s in both.
I'm going to take Spanish for A-level (would've taken French too but I don't actually want a career with languages and I'm already going to take 4) and I dropped geography before GCSE so I'm definitely biased, but I strongly think you should choose Spanish. Don't let these people put you off! If you truly love the language you should have no problem, one language GCSE is compulsory in my school so a lot of people aren't enthusiastic about it but still do well. I think you'll do great at Spanish and enjoy it too!
One extra thing, you might not know what you want to do after GCSEs but carrying on a language afterwards is seen as a really good skill that stands out and will be taken notice of. I want to do computer science at uni so Spanish is technically irrelevant to that, but it's nice to have something different to my maths and computer science options.