"My boyfriend is going on holiday with his best friend. Who is a girl he's slept with."

I have a relationship dilemma, and I don’t know what to do.

On Wednesday night, my boyfriend Matt* took me to a fancy restaurant to celebrate our first anniversary.

I was flattered that he took me to such an expensive place, but could see all night that there was something distracting him. After an hour of him uncomfortably shuffling in his seat, he finally spat it out and I couldn’t believe what he said.

“I’m going on a ten day holiday to Fiji with Jess*,” he said while staring intently at his steak.

My heart sank. Jess is my boyfriend’s long-term best friend. The girl best friend. While I’ve only been around for months, Jess has been Matt’s confidant and accomplice since high school. With blonde hair and a sassy (sometimes rude) give-no-f*cks attitude, she’s the complete and utter opposite of me.

And I can't stand her. Her mere existence as my boyfriend's best friend kills me, and I can't help but feel like their friendship is more than just a friendship to her, and that she doesn't like me because we're in love with the same man.

I'm an incredibly jealous person because I've been cheated on in the past, so hearing her name constantly pop up into conversations eats away at me, especially because I know she and Matt have had sex before.

Matt keeps saying that she's going through a rough time - she lost her job and her mother is sick -and that he needs to be there for her, but I can't help but feel something more will happen. He's constantly reminding me that he loves me, that he wants to be with me and that Jess was no more than a drunken hookup when they were teenagers, but I don't know how I will survive the ten days he's away with her.

When Matt has news about his life, he will call Jess before he even bothers to text me. They're constantly snapchatting and messaging on Facebook, but when I bring these things up he says he sees me more than her, and that I'm reading far too much into everything. He says he wants me, and there's nothing more to it.

Am I unreasonable if I give him the ultimatum of me or her? If I tell him he can't go I'm worried he will always resent me, and it will slowly pull us apart.

If he goes, am I daft for staying? Fiji is a romantic location, and everyone will be mistaking them for a couple. I feel sick at the thought of being so badly burnt by love again.

I love him, and I want to trust him, but there are so many red flags I just can't turn away from. I'm hurt and upset, but I don't want to make a hasty mistake I'll grow to regret.

What should I do?