if your questions is what will happen when you're reunited, then how does fear play in? what type of spread did you use? do you remember the other cards?
3 of cups for me in a relationship reading is the "dating" card, it's about happy times and not stressing and not being to serious.
So his fear can be you won't take dating seriously. Or that he'll lose his freedom, as many commitmentphobes do.
Some read it as a third party, but doesn't mean that there is another woman/man, but it can be the fear of interference from a friend or your mom per say. Or that he may feel you still have romantic feelings for someone else and can swoop in and change your dynamic.
Generally this is a happy card , one of celebrations and good things, I've also read it as a desire for threesomes
lol but again that all depends on the context of the reading.