To think anyone is obligated to do anything, even in a relationship, is likely one of the key drivers to the divorce rate and abuse in this fair country.
That said I'm going to say different strokes for different folks. Some people are just built that way. In my experience most are not. Shit like that only builds resentment over time which leads to separation in the long run. I've seen it happen with far too many friends to dismiss as coincidence at this point. They usually stay together only long enough for kids (if they're involved) to get out of the house then it's game over.
For most men, having sex I don't think has anything to do with feeling loved.
Note: I am not a licensed psychologist, I just play one on TV.
What's the point of being in a relationship if there is no obligation to your significant other? May as well not be together.
