I'm engaged but have a serious crush on someone

Hello. Im 23 and I'm engaged to my 31 year old partner, we've been together for nearly 2 years and have lived together from the start. I feel really secure, we have 3 cats together, a nice place and he's got a good job. There's no reason that I'm aware of that I should be looking at other people. Ive been in a few serious relationships and have never looked at anyone else with attraction whilst in a relationship because I'm usually very loyal naturally. However, I met someone and I can't stop thinking about him. He's a ticket gate worker at the train station, I've seen him for about a year and he always says hello, asks how I am, about my day and his day etc. Just basic friendly conversations. But I've never seen him do that with any other customers going through the ticket gates. It feels nice, feeling special, like a random person cares about me and wants to check I'm doing ok. So this has been going on for about a year, however in the last month or so, I've noticed I've started hoping that he's working whenever I'm getting the train, and I've realised how disappointed I feel if he's not there. And now I can't stop thinking about him and I want to go get a train just for the sake of it for a chance to see him. I don't even know his name, if he's single or anything. Also I think he's 40-50 years old... which has always been way too old for me, yet I see past that with him. He's just so nice and makes me feel happy and I get butterflies after seeing him. I'm hoping I'm just confused and my brain is getting mixed up between having a crush or just really liking someone as a person. I feel so guilty because I'm engaged, but I have no control over this. I obviously wouldn't act on anything unless I ended things with my partner but that's not an option in my mind. I just don't know what to do with these thoughts, they're only getting stronger