I suspect that he won’t be destroyed if this ends. Not only you deserve to be with the right person and be truly happy but so does he. He’ll find the right person eventually so he’d not be destroyed

It seems that you are already dating someone else. Even though it’s platonic and isn’t cheating, you go on regular dates, see a lot of different things together, enjoying his company more than your boyfriend’s, he’s interested in more with you etc Not sure if your boyfriend met a guy and if he ever joins you two or if he even knows about him but it does sound like beginning of dating someone new to me.

I think I’d have a conversation with your boyfriend. Living together complicates it but people split all the time. I think it’s better to end it now rather than waiting any longer. Especially if it’s already ended in your heart and you are enjoying another guy more.

Good luck