NO ONIONS?

So I love to cook and I think I am a pretty good cook, only problem is SHE doesn't like one of my fav ingredients that I like to cook with! Now we have been together TWO YEARS and I have done some bending on thing I never liked , for example yellow mustard on a hamburger, who the hell came up with this one? OK so we go to Mcdonalds drive thru a few weeks back of course I order mine without mustard, do they listen, NOPE...so i am stuck with it, and I have to admit it really didn't taste to bad, so we went the other night I had it agin, pretty good (actually I didnt even taste the mustard but it was def on there. My point is, when you are in a serious relationship shouldnt you try to do things that you may not like, but you know if you do them you will make the other person happy? And since I now do the mustard thing should she not at least try the onions?