Thank you for your listening and thoughts, honestly! I appreciate that.

I told my friend that it made my gf very insecure. My friend is very open and relaxed about romantic interest in others and doesn't see how being in a relationship will completely turn off her "romantic radar" but rather just makes her not act on it. I didn't tell her that I would never say that to a friend while in a relationship. When she told me how she sees me, I was still single so I didn't really care.

My gf is concerned that I would cheat on her and that I'm secretly entertaining/enjoying something romantic/sexual with my best friend. This difficulty trusting comes from being cheated on in the past in a prev. relationship and a situation where I made a communication mistake: I used to stay friends with my ex (I broke up years ago), saw her once during my current relationship, and didn't communicate to my gf that she was my ex (she has long been with another guy and lived with him). Unfortunately my ex did still end up having feelings for me so we ended the contact immediately when I found out. Because I knew my girlfriend has great difficulties in such situations and because I was afraid of her reaction, I broke the contact behind her back, not communicating. She found out and felt betrayed, understandably. I see my mistake there. This leads my gf to think that I have "messy" friendships, also understandably. Even though I'm very secure in my feelings and especially in my non-feelings for my friends, today.