There are worse things than leaving a lover if the relationship just isn't working for you on so many levels any more and it's not changing no matter what you try. Maybe it's time to let your connection with your bf go. I know that probably sounds ridiculously painful and impossible, and the idea of hurting him probably seems worse than hurting yourself, but you can posion yourself if you feel like you're always lying, pretending, hiding. It can really erode your happiness and self-esteem in ways that can take a long time to heal. He wouldn't want that for you, right?
I am not thinking of this as a poly thing, for the record. Poly has helped make it clear, in that your relationship with your gf shows you how much is missing with the relationship with your bf. But it seems to me like this isn't an nre issue, this is about something being fundamentally off with your relationship with your bf. Maybe it's because he's a guy or maybe it's just that the you/him dynamic has run its course for you. I've been there, and I took about a year too long in finally leaving, and I can tell you that that year really messed me up.
I am only giving such severe advice because it sounds like you've tried everything and are at the end of your rope. I may be wrong, of course, but sometimes I think it helps just to be affirmed in knowing that leaving is an option. Your life will go on and so will his, and hopefully you can even be friends and still benefit from his presence in your life, even if not right away.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.