That depends on your definiton of dating.
If with dating you mean "going out from time to time with nothing serious happening"than yes you don't have to be in love with him but if you mean dating as in "in a relationship".
well call me high standard but I prefer to only be in relationships with guys I am crazy about and I would never be with a perfectly nice guy who really wants to be with me and give him hope when the whole time I know I am in love with someone else!
I personally have a problem with that concept!

I's rather be single than be with someone I am not in love with and where I am aware of that fact just so to not be single!especially when I know I am still in love with someone else!