Am I overthinking this friendship dynamic or is something actually off?

I have a male friend I’ve been close with for about 9 months. We’re genuinely very good friends, and we’re pretty open with each other about most things. I would even go as far to say that we are some of eachothers closest friends.

To add context, this friendship always had a slightly flirtatious undertone on his end (which I didn’t really reciprocate). He admitted a few times that he had feelings for me, but we never acted on it until about two months ago. We ended up having a short talking stage/situationship/ whatever you wanna call it that lasted around a month.

We mutually ended it because we knew it wouldn’t work in the long due to our different backgrounds and other personal reasons. I'll honestly admit I was somewhat upset the day after because it just happened out of nowhere, but since then it's been fine and I'm honestly not heartbroken or anything like that because I don't think I was really in love with him like that. Despite this, we agreed to stay friends again and everything went back to the way it was before.

Recently, he started talking to a new girl that he seems to really like and I'm genuinely happy and supportive of him, and give him advice here and there when he asks for it, and I appreciate that he was honest with me about it, especially since we’d just ended things.

Hes had his fair share of talking stages in the past, but I've only just started to realize now that whenever he’s talking to a girl, he barely talks to me. When he isn’t talking to anyone, he becomes much more attached and talks to me a lot. As of recent, he only mostly reaches out when the girl he’s talking to can’t call or isn’t responding. Even when we do talk on the phone, he’s usually just texting her the whole time whilst we are trying to have a conversation.

It just makes me feel like he doesn't truly view me as a friend but more so a backup person that he can turn to only when he's bored or has no one else available, because honestly, I would prefer that he doesn't start to get so attached to me when he's done with another girl.

The issue is I really can't tell if I’m overthinking this because of our past fling and that I may be jealous, or if it’s reasonable to feel uncomfortable with being treated like a backup option in a friendship I genuinely value. But it honestly does feel like something's off.

I would appreciate any advice or outside perspectives 🙏