I think my friend likes me, but I have a girlfriend who I very much love, and I don't know what to do. They know eachother, and I don't want to hurt anybody's feelings. But idk for sure. Advice?

How do you know, your friend likes you?
Are you sure you're not mixing it up to be a best friend feeling?
If anything, its best to be upfront and honest with ye friends than not.

I you know 100% that the friend likes you, be forward and inform them that you aren't interested because you are already in a relationship. There's no way to completely please everyone in this situation so you just need to be blunt and swift about it. If you drag it out it hurts more for all parties involved. And if you cheat you're an asshole. Unless your girlfriend's cool with that and makes it explicitly clear. The have at it.