This perplexing phenomena is due to neural prostheses similar to Scratch-'n-sniff stickers, because the brain is made of science.
The olfactory nerves in the nose send information on the scent to the primary olfactory cortex of the brain. the cortex is linked to the amygdala and hippocampus of hte limbic system. The amygdala is involved in emotion. It projects fibres into the hippocampus. The hippocampus is involved in long-term memory. This is why smells evoke memories
All smells stimulate memories! Odor is a powerful memory trigger. Many times, just a faint scent is enough to remind you of something that happened years and years ago. Surely you can think of some specific summertime odors that remind you of something!
The olfactory bulb is an area in your brain that receives and processes smells. It is located very close to the limbic region, which is thought to be the reason that certain smells can activate vivid memories and emotions.
Perfumes are volatile, they give off invisible gasses which are made of tiny complex molecules, all different shapes. These little shapes float in the air. When these shapes go up your nose they fit into certain receptors in your nose which match the shapes, and Hey Presto! You recognise the smell! Different people prefer certain smells to others. Smells often evoke memories and the feelings associated with those memories. If the smells evoke nice memories, the perfume is appealing. But sometimes, for various reasons, some perfumes do not smell very nice. But this is all in the mind nose!
All of our senses except for our sense of smell. They are controlled by a separate station, the olfactory bulb, which explains why certains smells seem to do such a good job at bringing back certain memories.
smells are hardly ever tested via exams. smells are generally not trusted.
it means it can bring up old memories
* Yes it is possible (some do and some don't depending on why they split up.) For most people the couple have loved each other once (or thought they did) and built some fond memories together so it's highly possible your ex thinks about you off and on because sometimes certain places (even certain smells) can trigger memories that they connect you with during your relationship together.
Smells are caused by specific chemicals.
Spending time in nature can create lasting memories due to the sensory experiences and emotional connection it provides. The sights, sounds, and smells of natural environments can trigger vivid recollections of past experiences, making memories in nature particularly powerful and meaningful.
Largely it is to add their scent to the scent of that spot, to take ownership of a place that smells particularly nice to them.
Memory links to smells are some of the strongest memories, and once you experience a particular smell, you will most likely remember it decades later.