More romantic people tend to be vocally in favor of more romantic fidelity in my experience. If you think about it though, faith in romance is not a very romantic ideal. True love should overcome all things! The highest mountains, the furthest distances, social classes, families, inconveniences, ugliness, but NOT previous love apparently. There shouldn’t be any competition there. The love that got there first is automatically the better one, winning the support and protection of the sentimental against all other love on offer. Other impediments are allowed to test love, sweetened with ‘yes, you must move a thousand miles apart, but if it’s really true love, he’ll wait for you’. You can’t say, ‘yes, he has another girlfriend, but if you really are better for him he’ll come back – may the truest love win!’.
Perhaps more commitment in general allows better and more romance? There are costs as well as benefits to being tied to anything though. Just as it’s not clear that more commitment in society to stay with your current job would be pro-productivity, it’s hard to see that more commitment to stay with your current partner would be especially pro-romance. Of course this is all silly – being romantic and vocally supporting faithfulness are about signaling that you will stick around, not about having consistent values or any real preference about the rest of the world. Is there some other explanation?