Boyfriend at dinner with another female 'friend'

So I've been with my boyfriend for 3 months now and things were going well until he said he was going on holiday for a week with another girl that he'd never even spoken to me about, just him, her and her parents. I thought it was really strange but we spoke about it and it was resolved. he told me she was just one of his oldest friends but because I've been cheated on and have been in bad relationships in the past I overthink and start to doubt myself. Tonight he said he's going for dinner with her just them two alone and I don't know how I should feel about it. I don't think I have an issue with trusting him particularly, more just men in general really, but he's also quite closed off. He never really compliments me, nor tells me how he feels about me which isn't something I require all the time but I'd be lying if I said I wasn't somewhat insecure and occasionally just needed a "you look nice". So basically am I overreacting with this dinner?

As a male person, I found that situation very disrespecting and embarrasing. I've never had a relationship yet (I'm 19 years old) but if I had a girlfriend I would NEVER do that to her even though that female friend is my one of the oldest friends.

Why don't three of you have a dinner together? He should introduce you to this girl as his lovely girlfriend. That sounds perfectly correct to me.

Yes but have a look at the original thread! He is clearly trying to date both of them! She should never allow him to get away with doing that. The other girl is not her problem ! It is his behaviour that is the issue and she needs to deal with it. Having dinner together as a group of 3 will solve nothing; it will just complicate things more. She needs to set boundaries in what she allows him to get away with.