If it's supposed to happen, it'll happen.
“Taking things slow" just means you need to get comfortable with each other and see if a relationship happens.
The best relationships “just happen". They aren't forced. They aren't arranged. They just happen. 2 people start to fall for each other and they go from there.
However, remember this: you need to talk to your person about if you're taking things slow but still staying loyal to each other or if y'all are keeping your options open. That's very important. If one person of trying to take things slow and staying loyal with that one person, that means they already don't want anyone else but you. If you're “taking things slow" with that person and you're out talking to other people trying to pursue relationships with them too, it can come across as a slap in the face.
If you are supposed to be with that person, you'll be with that person.
Not to mention, if you take things slow, keep hanging out, keep things interesting, the more likely you are to keep a spark going. It makes things interesting. It makes every little detail so important because it can either be a sign y'all are moving forwards or backwards.
Good things take time. Love doesn't happen overnight. The happiest couples don't happen overnight. You have to work for it. You have to create it.
It's possible that one person may fall faster than the other one when taking things slow too. That's ok. That's normal. You both won't always at the same pace. Remember to talk things out. Communication is crucial in any relationship, but even more important when you're trying to make a relationship at a slower pace.
Also, remember if you take things slow with someone, things may not work out. This can be a good thing though. Would you rather take things slow with someone and end up not being with them or rushing things and make a mistake on the way only to end up not being with them?
Your person is out there. I promise. Don't rush it. They'll come when you least expect it. Just let things happen. Don't overthink it (I know easier said than done) and don't get into your head saying “they don't want me or else they'd be with me", “they probably have doubts", etc.