Feelings towards a co-worker

Hi!

Will try to explain this a bit simple, but not sure I can...

So I have been working in a office for about a year now, not a large office, we are about 15 people there. So the last couple of months, i'v gotten interested in one of the girls there. The interested has increased the last weeks a lot. I am not quiet sure if it is in my head or if shes interested too. But there have been serveral moments where I feel she also give me signs...

Sometimes the office starts with a coffee in the morning for a quick chat, and often me and the girl can end up sitting there talking a little bit longer then the others. There has also been moments when I am about to leave, she kinda keep the converastion going. Other moments she can come to my office, without not really going to talk to me about work but someone else, and stops by with me, just for a chat. She also gave me compliments last workday and was joking around a bit. She also once changed seats in meetings to sit closer to me, even tho I came into the room later then the others, and she already was sitting. On my bad days at works, I feel like she really notices and try to make me feel better...

I don't really know... but the real problem is... that she got a boyfriend...

And I don't want to destroy any relationship, so I will try to shut down my feelings. But I feel like I need to avoid her a bit to be able to do so... but how can I do it, without being a jerk of a co-worker?

Thanks for reading, not sure if it is possible tho, would love tips!
How not to destroy any relationship, while shutting her out, without being a bad coworker.