Just how often were you messaging one another? Were you a confidant to him? I differ here from the others in that your mentioning texting is huge tip-off to me. I am of the opinion this is inappropriate from the start. Sorry, that is just the way I feel. No doubt this is based on previous experience. I also want you to consider what was the nature of the relationship history he has with his girlfriend. Were you the only female he communicated with or has he made a habit of this? I point out that you don't know the whole backstory here as to why his girlfriend was upset or uncomfortable. Finally, please don't take this all personally. This is an issue between her and him not he and you.