I've been freaking out all day about this and I don't know what to do ?

Me and my boyfriend have been together for 2 and a half years and are madly in love with eachother. Recently he came on holiday with me and my family but as soon as we came back I went on his phone and found out he had been texting another girl before we left . They were only messages and he had never met her before and the messages were not that bad ( she was trying to convinse him to have sex with her but he said he didn't want to ). I forgave my boyfriend but he still feels really depressed about it . The problem that I have is the fact that from the texts I found out that the girl he was talking to was 15 pretending to be 17 and already in a relationship . Her boyfriend is 23 and she sneaks out of her house to take drugs , get wasted and have sex with many other different men . I'm actually discusted in her not only for what she tried to do with my boyfriend but what she is doing with her life . Am I wrong for thinking this ?