I had something like this happen in a relationship of mine once.
I was with someone who I thought was a dominant/top, who very effectively hid the fact that they were a sub-leaning switch until our honeymoon. Now, being the open-minded sort I am, I was less infuriated than I might have been, but I was still very miffed, because that's kind of one of those things maybe they should have told me, oh, any other time before we got married. You know, just in case I was in fact not cool with it. It very badly affected our relationship, because I wasn't that far along my journey yet, hadn't developed much of my more dominant side, and usually preferred to bottom. They were also a terrible do-me sub, which is where my distaste for those types was born. You'd think they'd invented topping from the bottom, so they weren't all that much help on my dominant path anyway, as they never did actually let me exercise it other than to their desires. Yeah, it was like that. A lot of other things were wrong with that relationship, I in no way blame that whole disaster on our both being switches, but kink and sex and roles and expectations became one of the major inflammatory points between us, and each problem led to another. I'm thankful it ended some years ago, and though I still had some growing and learning to do (it never ends, of course) I had definitely learned a lot of what was not right for me in a relationship. I'm not sure if that relationship was the cause of the trouble, since it was almost my first kink+ relationship it's hard to say, but I've never been able to have a dynamic with a switch as a bottom since.
I've thought about it a lot though, and I believe it's more the fact that as an s-type I'm very much a challenger, very into the power struggle. When I'm in what is meant to be a dynamic where I'm submissive (that's a long story) I push, and find safety and a sense of comfort in being put where I'm supposed to be. It's hard enough for the D-types, but when it's a switch, it's even harder, since half the time I end up pushing their s-buttons, when that's not what I'm hoping for at all. The only person I've ever been submissive to in my heart is my current Master, who knows just how to do what I need him to do if I start getting feisty, which is very rare on account of his energy and the nature of our connection and dynamic. That's one of the ways he captured my heart in the first place.
One of the very wonderful things about being poly is the fact that my different partners all fulfill very different needs and facets of my personality. It works out wonderfully for me, but I know poly isn't everyone's cup of tea. I do know people who have dynamics without what would traditionally be called romantic or love connections, though, and I know in some cases that can work out for people who aren't poly but still need something their partner can't or won't give them but would be alright with them having with someone else. It all depends on your relationship, your comfort levels, your needs, and the people around you who might be willing and able to help if you choose.