He received oral sex off someone else while we were dating?

Myself and my boyfriend have been together well over a year now, but sometimes I think back to when he got oral sex off a girl a week before we became official! I know it's stupid and it was ages ago, but what are your opinions on it? It (the oral sex he received) happened at a house party of which all of my friends attended (who knew me and him were dating), however, I didn't go as I was ill. The things that hurt the most was that all of my friends knew and didn't tell me that it had happened, the girl it happened with came up to me a few days later in a night club and apologised to taunt me however, she didn't state what for, leaving me confused. And he didn't confess until nearly two month later. 
What are your opinions?

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