My good friend gave my ex-boyfriend a ********? how should i feel?

i have only had 2 boyfriends in my life, one being very serious. we dated for a very long time, and we lost our virginity's to each other. we broke up about a year ago, but as we all know it's hard for a girl to move on from her first. a few weeks later, my best friend at the time decided to try and talk to him. i knew she developed feelings towards him while we were dating but i didn't think they would go anywhere. they started talking, and went on a few dates, but the farthest they went was just a hand job. still, i was very upset because this was weeks after i lost my virginity to him! it took me a while to get over it, but i eventually did. now, my ex and i are good friends. but as of a week ago, i've been told she started talking to him again. they've gone to the movies and hooked up a lot apparently (not sex). yesterday, a group of about 10 of us went to the beach. the two of them joined. she was clinging to him the whole day, which he obviously didn't want. he gave me a piggy back ride and we were goofing off in the water, which we could all tell she was very upset because of what she was saying and her facial expressions lol. soon after, she asked him to go to the car with her to get something. according to one of my guy friends, my ex told him she gave him a ******** in the car, the first time she ever did that to him. i feel like she's very insecure and feels that there is a competition between the two of us as to who can have him. but i dont want him! we're just friends and i think she thinks he's not gonna like her anymore...but the truth is, i don't think he's ever really liked her. i think he just hangs around her because he gets some action. she wants a relationship, but he's obviously not going to give her one if he can get all the physical aspects without the title. am i right? yes, i was upset that she did something like that, even though we broke up a year ago and i have no feelings towards him. why am i feeling like this?! and what should i do? am i allowed to be mad? please help!