My (24M) friend (25M) said “I love you too” to my girlfriend (24F) and has been making subtle comments that feel boundary-crossing. How should I handle this moving forward?

We were all hanging out for the first time for an extended period, just the three of us. During the night, my friend started talking about how attractive he is. He went on about how both men and women are into him and concluded that this must mean he’s objectively attractive.

At one point, my girlfriend casually mentioned that girls tend to like her because she dresses a bit more masculine. He immediately jumped in to affirm her, saying that he likes that and that she’d be someone who is objectively attractive too.

I didn’t say anything in the moment, but it rubbed me the wrong way. He tends to become more performative and attention-seeking in social situations, especially when I’m with my girlfriend. It felt like he was subtly trying to position himself as desirable in front of her.

Later, when I dropped my girlfriend off, I told her I loved her and she said it back. Then, in front of me, my friend said “I love you too.” He made eye contact with me and immediately apologized. It felt like he was testing my boundaries. That moment didn’t sit right with me at all.

I confronted him about it later and said it crossed a line. He seemed surprised and said he didn’t mean anything by it. I ended up softening my stance in the moment, but I later followed up with a message explaining more clearly that I felt uncomfortable and disrespected by the way he acted.

My girlfriend doesn’t think he meant anything by it and feels like I might be overanalyzing. But I don’t think I am. Social dynamics matter. I felt like he was inserting himself into a space between us in ways that felt off. I know she tends to be a little oblivious when someone is flirting or trying to get attention, so I’m not sure how to approach this with her in a way she’ll fully understand.

I’m not trying to be controlling. I trust her. But I don’t feel great about how this all unfolded.
How do I move forward with this, both with my friend and my girlfriend?

TL;DR:
My friend made some boundary-pushing comments while hanging out with me and my girlfriend, including saying “I love you too” to her after I did. It made me uncomfortable, and although I addressed it, my girlfriend didn’t think it was a big deal. I don’t want to overreact, but I also don’t want to ignore it. How should I proceed?