Lesbian fantasies?

I’ve been with my partner for 12 years (since we were 17) and I’m straight as far as I know lol. I don’t have any desire for a relationship with a woman but I really enjoy watching lesbian porn and sometimes use the thought of having sex with a woman to please myself vs thoughts elsewhere. He would be fine to know I’m having these thoughts because he’s very confident in our relationship and so am I but I find that I’d rather keep it to myself. I’m so in love with him, but I really do fantasize quite a bit about having a friends with benefits with another woman or sexting. It usually mostly happens certain times of the month and I’m not a super sexual person so it’s very weird for me right now.