In that case it is difficult to find out if Michael was married altough I think he was not. I found Scott Edgar on FB and left a message on messenger. Maybe he investigated more men of the 1st Bn Airborne Royal Ulster Rifles. I am not giving up yet.
There were very few marriages in Ireland (Irish Free State from 1922 then Republic of Ireland or Ireland) with a bridegroom named Michael Thompson in the short timeframe when "your" Michael may have married. (Michael and Thompson weren't common name combinations in Ireland. Your Michael was the only one born in the whole of Ireland in 1918.) The marriage registrations can be viewed on Irish Genealogy website. It's free. You need to sign in each time you use it and prove you're not a robot. You can also search for death registrations of Michael's parents if they remained in Ireland (Irish Free State which became the Republic of Ireland) and died before 1970. That search would take longer and may be inconclusive.
https://www.irishgenealogy.ie/en Birth, marriage and death registrations in the 6 counties of Ulster which became Northern Ireland after the partition of Ireland in 1921 are at the General Registry Office of Northern Ireland (GRONI). A search for records there is different.
Explanation:
https://www.irish-genealogy-toolkit.com/Northern-Ireland-civil-registration.htmlIrish Genealogy Toolkit is a good introduction to Irish family history. Lots of advice, tips and links.
If Michael did marry, it may have happened in Britain. It was common for young Irish people to go to Britain to work and live. The Royal Ulster Rifles did wartime training in various places in Britain.
Added: Edited information about Northern Ireland records.