Andrezza, I was caught off-guard with the question! One would be tempted to think in terms of "sleep", since the topic has led into this direction.
But I think it was in general terms (as we say here in Brazil more often than not to other things). So, I thought long and hard on it and came up with that expressions:
If I want a boyfriend/friend just for the sake of it.
I won't ever have a conversation just for the sake of it. It should have something relevant/interesting/useful, etc...in it.
Oh yeah I go out when the vibe is right, I don't go out just for the sake of it like many people do, I guess.
I don't go to places just for the sake of it.
There is, in general terms "...just for the sake of it" would do. Of course, with the first sentence it could mean both, romantically or in general terms (there is, said in a matter-of-fact way).
I hope that helps. Ah, and certainly there are other ways to express that, so let´s wait for others to chime in.