I need help desperately

I’ve been with my boyfriend for close to 5 months and we have sex pretty frequently. Problem is, he has quite the ‘advantage’ in his pants if you know what I mean. Well above average. Before him I had never been with anyone with a dick over 5-6 inches so I was fine with that, but it takes a very long time to adjust to him now when we do have sex. Don’t get me wrong it’s enjoyable every time but almost every time recently, before we have sex I’m super anxious and almost try to get out of it because I know it’s going to hurt to adjust to him. We’ve been having sex for probably 7-8 months and I still can’t get used to it. He says I’m really tight and he has no idea how I haven’t adapted since it’s so frequent. I don’t know why either. Will I ever ‘loosen up’ to fit him? I don’t want him to feel bad about this if I tell him since there’s quite literally nothing he can do to help me. It’s not his fault and he’s so so sweet about everything when we’re intimate. Does anyone have any ideas on what to do here? Even on getting anxiety before having sex? I’m so lost here, any help is appreciated ❤️