I'm posting to get some etiquette advice regarding meeting a male school friend (let's call him Tom) after a long time (around 15 years). There is no complex backstory, and our friendship was always strictly platonic. We were good friends at school (lots of friendly banter and shared academic interests) but did not spend time together outside of school, know each other's families, etc. Tom moved schools during our GCSE years and we did not keep in touch (I remember wanting to but felt very awkward at that age asking for his phone number -- very silly in hindsight, I know). Tom did keep in touch with some male classmates who have also remained friends with me over the years (I was lucky to form closer connections with these other friends during sixth form and university), so I have indirectly heard about Tom on a very infrequent basis.
Now, I have just heard from our mutual friend Bob that Tom has recently moved to the city where I currently live (it is in a different country from where our hometown is, and I don't have any very old friends here, so naturally I felt very happy about the prospect of seeing Tom again.) Tom's fiancee happens to be from this city, so Tom worked out a job transfer to be with her. Bob said Tom remembers me and is also interested in reconnecting. Bob gave us each other's contact information, and I plan to message Tom in the near future (I'm currently travelling for work). I am very excited, as Tom was a friend I really enjoyed spending time with in school, and I hope he is still as witty and fun as he used to be.
Would it be socially proper for me to ask Tom to meet for lunch or coffee at a local cafe, for example, without explicitly inviting his fiancee? (I have never met her of course; Bob said that she and Tom met just a few years ago as working adults, not as school/university classmates.) I certainly want to get to know her and be friends with her too, but I'd love to meet Tom alone first and reminisce about our school days, and see if he is still the same person I knew in school. Would it make him or his fiancee uncomfortable if I only asked Tom to meet with me? I ought to be thankful for her existence because she is the sole reason Tom moved to my city in the first place! I am happily single and wouldn't be romantically interested in Tom even if he were single, but I recognise that others may not see it that way. Since Tom and I are no longer 15-year-old children but adults around twice that age, should I treat Tom and his fiancee as a single unit by default and not even consider asking Tom to spend time with me alone, regardless of whether it's the first time we reconnect or future meetings? And I fully understand that life is different now and Tom may have changed a lot from our school days, and it would be foolish of me to hope to re-gain the exact same flavour of childhood friendship I once had with him, but I want to be optimistic and socially appropriate to maximize the chances of building a solid friendship with him and his fiancee. I know I wouldn't be asking this if Tom were female like me, but it's the first time I'm reconnecting with a male friend like this and don't want any wrong impressions to be formed.