Your professional space
The relationship itself isn't the problem if you met before and you know how to be discreet and professional and don't make out in the open-plan office.
The problem is usually when you meet someone at work and after a while it turns out to be a dud. That can bring resentment, unprofessional behavior, hostility and personal conflicts. It's best to keep your professional space yours alone and focus on work at work, not on building romantic relationships.
Affairs
If you've seen a few movies in your life, you can surely guess that an affair is a really lousy idea that leads to a lot of stress, trouble and guilt.
Sooner or later it'll all blow up. Bumping into a friend on the street, a notification on your phone, or even something as unexpected as a speed camera photo can give away your dirty little secret.
If you think nobody at work can tell because all you do is sneak a glance or give a subtle smile, trust me, they can tell.
One of the key things in a relationship is being loyal to each other. When you're together, you have your own world where you understand each other without words and trust each other completely. Breaking that bond for a passing crush is stupid and reckless, and lost trust can't be rebuilt.
It's easy to fall for someone at work, because we spend a lot of time there. But don't be fooled by appearances: it's only a slice of reality that can look very attractive. Everyone is nicely dressed and smiling, and there are lots of chances to interact. Hidden deep on the other side is the prose of everyday life.
The prose of everyday life
Keep your everyday life in balance. Make opportunities: take your girlfriend or wife out on a date, and afterwards live out your sexual fantasies together.
But if you want to go for a new relationship, first have the guts to end the one you're in. Respect the person you're with.
Working from home during the pandemic left its mark, because a lot of relationships lost their safety valve: getting out of the house every day. Overnight, people were stuck together 24 hours a day, and if you throw in stress and all the COVID restrictions, you've got a recipe for disaster.
That's why it's worth taking care of your quality time. Time you actually spend together, not just next to each other.