The key to happiness in a relationship may be having more sex, according to a new study.

It’s already well known that sex is good for bonding and releases the feel good love hormone oxytocin, but now researchers have found that it can release a 48-hour “afterglow” after you do the deed that keeps you feeling warm and fuzzy.

Scientists from Florida State University got 214 newlywed couples to fill out sex diaries for 14 days and asked them how they felt about their relationships. They then asked them to re-evaluate their relationships six months later.

What they found was that people had feelings of contentment about their relationship that lasted for two days after they’d had sex, but the feelings seemed to fade after three days.

The research was published in the journal Psychological Science, and found those who reported a stronger “afterglow” were most likely to be happiest in their marriages.

The researchers believe the results might be linked to men’s sperm concentration. Previous research found that when men have sex too much, their sperm concentration diminishes, but is usually restored around day three.

The theory is that the “afterglow” feelings could be nature’s way of keeping a couple together while the man’s sperm count recovers, which increases the chance of reproduction.   The maximum time sperm can survive inside a female is also two days.