Well, I can’t necessarily answer your question…but, I will give you this: you will receive “total consciousness”, so you got that going for you.
Seriously, sometimes I have a very hard time seeing intimacy as being viewed through the lens of a D/s filter. Sometimes – No – there doesn’t have to be this D/s component. Maybe he just loves you and by cumming inside you, he really is just saying it, with his actions. Four years is a long relationship by any standards and marriage would probably be a topic by now. It is natural that he wants to cum inside you, D/s or not.
Honestly, one of the hardest things for me is walking that fine line between “will this D/s piece help us grow” (i.e. submissive journaling, tasks, etc), or sexually, “will this subspace/aftercare/subdrop scene” bring us closer. The answer is No, if you don’t communicate Why you are doing things ahead of time and afterwards.
Communication – is the centerpiece of it all. So my advice is this: ask him, why he wants to cum inside you? Ask him, what it is that he likes about it? My guess is – you will be closer for having this conversation and end up fucking a very very very hot scene that night.
That, or just Gunga Galunga…