Should I just ghost him?

Background: I am in a long term relationship for 7 years (met young), not married, not living together but planning on it within the next few years. Recent Developments: I met a few (5) new "friends" through a work situation where we became really close but we all quickly went in separate directions. I like them all and we decided to keep up with each other. Out of the 5; two I chat with very briefly and short conversations, two I chat with in length but less frequently than the last who I talk to every day in detail. Problem: The last person has now become a constant in my daily routine without me really realizing it. It is most convenient, to me at least, to speak closer to the evening because then conversation is not fragmented. Usually our conversations are about our shared interests, daily happenings, family and jokes. But recently he has wanted to talk about a girl he potentially wants to date. For me at least it is uncomfortable because I don't think I want to get involved. My friends who I would normally talk to have been in my life for a VERY long time and I trust them completely so for them relationship talk would never be strange. I guess my unsettled feelings are from the whole concept of having a new friend, who is the opposite gender, who is quickly becoming very close. I know this may sound weird but I feel really uneasy. I don't know if it is because I don't have many "new" friends at all so I don't know what's normal. Or that its because of the gender thing and that I'm in a relationship so I feel guilty. Or that he's now starting to date and I don't know how to proceed. Last notes; I did tell him that I am very happy for him but I don't want to get involved but I think he thinks that's a joke..? I like talking to him but maybe this is just getting too weird? Any suggestions on what I should do differently or say would be greatly appreciated?