Good question. We are the same age, grew up in the same city, and have always been drawn to similar styles, so I don't feel like I am curtailed in any way by my partner's style preferences. There are certain things I know he particularly likes, such as rock n' roll boots, so that probably has some influence on how often I choose that sort of thing -- even though I like them already.
You say "romantic relationships", but for me there's only really the one. I have had the same romantic partner for so long now that I don't know how I'd feel if I were with someone else. I don't think my early boyfriends had any influence at all on my style, but I was young and headstrong, and I'm sure I thought that being influenced by a boy would be a sign of weakness! Haha. I dated a law school student once who wore very preppy clothes, which I thought was a bit dorky, but it was sort of cute. I was all grunge, all the way, and he didn't seem to mind. There was also this mathematician I dated, and he liked to tuck his shirt into his jeans, which made my fingers itch. I was always pulling his shirt out for him. (It didn't last).
Supposing I were on the market now, I don't think I would be attracted to someone whose style I actively disliked, but I could imagine liking someone whose style I was neutral about, or who had no style.