We all have been in relationships like this, right? When times are good — man, are they ever good. The laughs flow, the good times roll ... it’s not unlike that relentless, ubiquitous Bud Light commercial you’ve seen since the start of the NCAA tournament, a first date you know is speeding toward a second.

But when times are bad ... well, it can make you feel worse than those Allstate ads starring the guy from “Oz”: beaten up, bloodied, broken down.

The Knicks and their fiercest devotees have had that relationship for most of the season’s first 4 1/2 months. When the Knicks are playing well — and forget for a moment the quality of their opponents the last four games, they have played as well as they have in weeks — it doesn’t take a lot to unleash the fans’ optimism, their swagger, even their imagination.

And that’s funny.

Because when the Knicks are playing lousy — such as the four games immediately preceding the last four, and for troublingly long stretches of the New Year — you tend to have a lot of people who wonder if the Knicks ever are going to win another game. They are that kind of team, easy to fall in love with, easier to fall out of love with, inspiring the kinds of mood swings that remind you of ... well, love. And hate. And the slim boundary separating the two.

Which brings us to tonight, to this week, to a fresh chapter of this unfailingly interesting season. The Knicks play the Celtics tonight, and they meet again Sunday at Madison Square Garden, and both teams are missing substantial pieces: no Rajon Rondo, no Kevin Garnett, no Amar’e Stoudemire, probably no Tyson Chandler.