True or False?

Is it true that a relationship can get screwed due to the fact that two people spend too much time together?

I think it's very possible that at one point you get bored till death.
But on the other hand spending time with someone u like, love, etc. shouldn't be boring to death experience.

So thinking about that I am a little lost. What should a couple do to retain the itch of wanting to have sex with the other person all the time, not feeling bored and so on.

Blah, the more I think the more I get lost.