Let's assume this quality of existence happens spontaneously and see what happens. For simplicity, we'll focus our attention on New York City at 12-noon.
There's about 350,000 people walking in Times Square each day, which averages to about four people entering each second. According to Google Maps, it takes about a minute to walk from W 46th to W 47th street (one edge of Times Square). So we wind up with about 240 people in Times Square at any one time after the first minute. (This assumes no one stops to shop, chat, or gets held up by traffic lights.)
The 240 people (I'll assume none of these are in love with each other) in Times Square accelerate towards each other at phenomenal speeds, somewhere around the strength of attraction just outside the event horizon of a black hole. All these people die due to the sudden negative acceleration at the end of the short journey. We're left with a giant ball of human corpses sitting in the middle of Times Square. (Not to mention any unfortunate dogs, shopping bags, and cars that are dragged along by the flying humans.)
We now have large balls of human debris all over the world. In New York City, an uneven distribution of kinetic energy from the inbound debris causes our debris ball to start rolling. It moves down the street and meets up with another debris ball. They crush together to form a larger sphere and continue rolling in a new direction.
Cutting it Short
Things are getting pretty gruesome, but we don't really care anymore. The majority of the world's population is dead within the first minute. If we assume magical pull exists regardless where in the world a human is, then our debris balls will eventually gather up every human and countless debris items and, in the end, all merge together to form one giant human debris ball.
I don't know how much matter would be contained in the final debris ball, but I'm pretty certain I could find a few moons in the Solar System that would be smaller.
To Answer Your Questions
if everyone knows the trick will humanity still be in danger of collapsing?
Yes. The only way we don't all die from this is if everyone unconditionally loves everyone else all the time before the magic goes into effect. Which, were that to be the case, we would all accelerate away from each other at the same speed as we would have been attracted to each other and fly off into space (and die anyway). (This suggests there is a very fine balancing point somewhere in the middle.)
Or will true love overcomes any obstacle?
No. We're all dead, so we can't experience love anymore. This question is useless in the face of this scenario.
Will you still believe in love?
Again, no. I'm dead. I will, however, remember to take a number to punch Loki in the mouth when I get to Valhalla. ...and hope this magical influence doesn't extend to people in the afterlife.