What the contact does
Venus describes what draws you; Mars describes how you pursue. A square puts them at odds, which produces friction rather than agreement, and friction between those two reads as charge.
The trine version of the same contact is easier and consistently described as less compelling. That is the argument against treating hard aspects as problems in synastry: in this pairing the difficulty is the point.
What it does not describe is durability. A comparison with a strong Venus and Mars square and nothing supportive elsewhere is a documented pattern, and usually a short one.
How each side experiences it
The Mars person is drawn to the Venus person and pursues, but often in a way that does not match what the Venus person values. Too fast, too blunt or at the wrong moment. The Venus person finds that mismatch exciting and frustrating in equal measure.
That tension keeps attraction high for a long time. It also means arguments and attraction tend to arrive together, which some couples enjoy and others find exhausting.
What keeps it from burning out
A square between signs of different elements, fire against water or earth against air, asks each person to learn the other's pace. Couples who talk openly about what feels romantic to each of them usually keep the spark and lose most of the friction.
It is strongest within three degrees. A Sun to Moon trine or a Saturn contact elsewhere in the comparison gives it the staying power it lacks on its own.
If you have this contact
Learn the other person's idea of romance instead of assuming it matches yours. The Mars person may need to slow down, while the Venus person may need to say plainly what they want rather than waiting to be read. When an argument starts, pause before it becomes a contest, because with this square the urge to win runs high. Physical activity together, from dancing to hiking, is a good outlet for the extra energy and keeps the spark from turning into friction at home.
Questions people ask about this
Is Venus square Mars good in synastry?
It is one of the strongest attraction contacts. It brings chemistry with friction, so it works best when other contacts add stability.
Why do we fight and then feel closer?
The square links desire with tension, so conflict and attraction rise together. Learning to argue without scoring points helps keep the closeness.
Is the square stronger than the trine?
It is more noticeable. The trine is easier day to day; the square produces more pull and more friction.