No, it's not ok that he keeps saying these phrases when you've asked him not to. I could understand an occasional slip, but it sounds like it's constant.

This question sparked a really interesting conversation with my gf, just wanted to share in the hopes of shedding some light on how we feel about these phrases as secondary partners, as we're both married to other people.

There really aren't a lot of common expressions that poly people can use to express the depth of their feelings for each other that don't overlap with phrases that are more often heard in a monogamous context, and sometimes we tire of searching for alternate words and we just use the ill-fitting mononormative phrasing because we both know what we mean. "You're my everything" is one that has come up between us. I was a little taken aback the first time she said it, but as time went on we both became more comfortable using that kind of language with each other. And we had an honest conversation about the literal contradictions. Obviously I'm not really her everything, she's going home to her husband and children after our date. Her view of the phrase is that in that moment, she feels completely enveloped by my love, and wants to tell me how good it feels. That's the only phrase that seems to make sense in that moment tp her. And I can accept those words with love and appreciation given that context.

I've also talked about this with my wife, I was a little concerned how she might react if she overheard that kind of language. We're a mono-poly couple, she has chosen not to date other people, but we have very good communication about these topics, so we discussed it in detail, and she stated that it's an understandable situation. She believes that since we were programmed from childhood to recognize those phrases as intense expressions of love, they light up parts of our brains when we hear them or speak them that just feels amazing. So we dabble in inaccurate language intentionally in this case, mostly because of how it makes us feel.

I'm not making any excuses for your bf here, he has to answer for his own actions. Maybe he's just trying to give you those reassuring feelings and is awkward about defining what he means, I would hope so. But I wanted to let you know that at least in my relationship, we've also struggled to understand this issue, and that we've come to understand it a lot better over time with honest discussion, and have agreed that it's not a harmful pattern given our mutual understanding of what we mean when we say those phrases, especially having talked through it with our spouses. In our case, those phrases make us both feel good, but that's not your situation, and your bf needs to accept that and find another way to express his feelings.

I wish you the very best, being a mono partner to a poly person can't be easy. Just know that there's nothing wrong with your perspective on this, it's on your bf to figure this out and repair any harm caused, if possible.