What's happening to me? My girlfriend is driving me crazy

Good people I'm telling you something that's happening to me so you can help me and if it happens to you too My girlfriend showed me some bikinis she had before traveling to Cancún, but never used them because she was ashamed of showing too much. She said they were very small, but would look divine on her. I told her to try them and if they fit well, I'd... fuck her right there how beautiful she looked. The thing is that while we were on vacation, we got to the beach and when she took off her shorts, she was wearing that bikini! She never wears revealing clothes in public, but with that bikini, her whole ass was exposed. I felt like everyone was staring at her, there were guys all around us, and it gave me a cramp in my cock. She put sunscreen on her legs naturally, and definitely had guys looking at her fixedly. She walked to the water and I kept gazing at her ass. And by the way, I told her to take some pictures. I kept feeling like men were staring at her ass. She'd look back and if they were looking, it really got me hot knowing they wanted to... with her. Is this normal? What should I do? Here are photos.