Shaun's reference is a really interesting one. I still don't see an obvious connection between 'Weert' and "Lisse" (as Treetotal suggested).
One possibiility is that "Lissen" might have been a misspelled (phonetic) reference to the the village of "Liessel", about 30 KM North of Weert and 6KM South of Deurne.
On the 22nd of september 1944, the Suffolk Regiment of the allied forces freed the town of Weert. On the 24th, the regiment freed the town of Deurne . The village of Liessel would most likely have been 'enroute' between Weert and Deurne.
At this stage of the war, the allied forces were still pushing a small 'corridor' northwards up from Belgium, through the Dutch provinces of Limburg and North Brabant towards Nijmegen.
A third possibility is that your father met Jan van Lierop in Weert and they were together when the allies freed "Lisse" (april/may 1945).
Personally, I think the Weert/Liessel connection is much more likely both geographically and in time.
In 1944, a major priority would have been to keep 'the corridor' open (safe) and the supply lines operational. Men would have been deployed to keep the logistics running smoothly and -where possible - to gather and utilise support from the liberated Dutch population (labour, food, materials, transport, etc.).
Personally, I think it's likely that you father met Jan van Lierop either in Weert or in Liessel. I've no idea how long both stayed there but it seems long enough for a real friendship to have developed.
I would be interested to know whether the photo than Shaun referenced bears any resemblence to the "Jan van Lierop" in your photo.
I've lived in the Netherlands for 40 years (in North Brabant) and I'm fluent in Dutch. I've accessed Dutch genealogy resources now and again and I know where to find them. But all my ancestors are in the UK/Ireland so I don't use the Dutch ones much. But I would be happy to post a query on 'jan van Lierop (Weert) on your behalf. Let me know.
Mike