You had zero risk for anything with your activity. Not an std, not hiv. You can not get an std of any sort for kissing and sucking breasts. Kissing lips? Well, you could get hsv 1 but 80 percent of the planet has that. It's cold sores, fever blisters. That's it. HIV is only spread through penetrating vaginal or anal sex or sharing IV needles. So, this is not an encounter to worry about.
Greetings.
The kind of encounter you had is very safe: kissing can spread cold virus and COVID. nipple sucking is even safer.
There is absolutely zero risk for HIV - it doesn't transmit via nipple sucking.
There is no risk for any other STDs either, since there was no genital contact.
You should relax and move on. your romantic moment on the beach will not be shadowed by STD concerns.
Also, it is a bit hard to recall properly as it happened so fast and I was under the influence of a few alcoholic drinks but I just wanted to mention that there were no fluids or anything like that from her nipples/boobs from what I could remember.