Went swimming with my gf and I couldn’t handle her

Me and my gf went swimming with some friends yesterday and she looked so sexy in her bikini it was hard for me not to get hard and stare all the time I saw some other people stare at her ass too and I honestly loved it I was horny the whole day and when we came home and tried something I couldn’t handle it I didn’t even made it passed her cheeks and I came after 3min I was so embaressed