My gf always seems to be getting groped, she has large natural breasts and guys just can’t seem to keep their hands off them, the most memorable incident was when we were on holiday and visited a water park, there was a long stairway to the top of the slide and my gf became separated from me in the queue. There were a group of young guys between us and I could see that they were talking to her from my position behind. Then one of the guys started playing with the tied fastening on the back of her bikini top, the next thing I knew they had undone it and as she reached back to try to secure it they were grabbing her exposed breasts. I tried to push my way through to stop them but the stairway was too narrow. Although I was angry, I was also becoming aroused at the same time and had to cover my erection. When they reached the top of the steps and the opening of the slide my gf was sitting down and holding the safety bar as she waited for the signal to go, then just as the signal came, one of the guys jumped forward and positioned himself directly behind her with his legs either side and his arms tightly around her waist, I knew he would be groping her all the way down, but couldn’t do anything about it. We talked about it afterwards and it turned out that she was just as excited by the experience as I was. That feeling of helplessness is so hot, you know what is about to happen, but you are powerless to stop it and can only imagine the parts you don’t see.