My fiance sometimes fantasizes about others?
My fiancé and I have had a very wonderful and loving relationship. We discussed this once before, but it got brought up again the other day. My fiancé said he isn't entirely against partner swapping/swinging, as long as both partners consent to it. I told him I would never want him to do that, just because it would hurt me too much. He says he is fine with not doing it, and that he will be happy with me even if we never try it. We are already a bit different sexually, as we do BDSM play frequently (he is the sub).
However, he admits he occasionally has fantasies and sexual thoughts about other people. I'm not sure if it is one person or multiple, but in my opinion, that isn't a good sign. I feel like if he truly loved me and was sexually satisfied with me, he wouldn't have any wandering thoughts. We have sex regularly and we both enjoy it. We also love spending time together and overall he is wonderful. I'm just worried that maybe he will want someone else eventually since he has told me this stuff.
Am I worrying too much? Is it normal for men to have fantasies about others even when they are in committed relationships? He assures me that he loves me and wants to be with me forever, but I just want some advice from other people.