Programs: AA EXP/CK; DL DM; US CP; Hilton Diamond; SPG Platinum; Hyatt Platinum; National Exec and others
As long as you travel to and from Cuba through another country than the US and use your Belgian Passport, no problems. Do NOT use US travel documents, and make no arrangements in the US or with US companies. Many of us who are dual citizens have done this repeatedly. NEVER use any US connection in any way in doing the travel and all will be well. The easiest ways seem to be through MEX, just because of flight availability, but most major European cities seem to have good deals also. i use MEX.
You are still covered by OFAC regulations and may have more at risk - it is easier for them to deny your green card renewal. But the risk is very slight - OFAC aren't interested in travellers to Cuba any longer.
I would agree that the only way to get to Cuba is not thru US, but through another country such as Canada or Mexico. Cuba and US are enemies, so make sure no ties or relationships with US to be mentioned.. nil.