Serious question for all men and open minded women too...?

The other day, my girlfriend performed fellationon me which in rare, becasue she hates my d**k being anywhere near her face. However, she disclosed to me she thought it was gross because her first time doing it was with her last boyfriend. This has been bothering the heck out of me. I know who this guy is. He goes to her school and is in her cl. I have to see him at all school functions she wants me to go to. I mean I know everybody has a past, i just didn't need to know any details. Now everything I see him, he has this kind of smug look, and I just start thinkin about how he had his d**k in my girl's mouth and its like i got his leftovers. I feel like a sucker. My pride is hurt so bad. I just envision him standing over her receving head. I want to beat his *** but I don't have a just reason. To all the guys out there would this bother you or not? And please no answers "like get over it" or "grow up". I need serious answers. Ladies too feel free to chime in.