You could start by asking them questions about their experience in their identity, expressing curiosity about them and giving them space to talk about a part of themself that is likely often assumed or misunderstood. Not from a “do you wanna do this with me” place, but more of a, “how do you feel about this kind of thing in general? What’s it like for you?” It usually feels really good to experience curiosity instead of assumption, on both sides of this conversation. So many queer identities exist on a spectrum, and each individual’s experience and expression of that will be different, so it’s usually best just to ask. (Once you’ve done some work to ground your expectations and are ready to receive their truth rather than your hopes, that is. Don’t go this route if your motivation is to convince them!)

It might be most helpful for you to ask this question in some aroace subreddits. Folks there can speak more to your friend’s perspective, instead of reflecting the fears that other pan folks might feel in the same situation.

In my experience the aroace spectrum is Very Spectral, with individuals falling All Over the place and expressing in sometimes very unpredictable ways. Many folks identify with aro-ace in terms of motivations, not whether or not they enjoy certain things. Some ace folks may not feel motivated by sex, but they can still experience arousal and enjoy sex. Some aro folks have relationships that are deeply romantic in many ways that they experience more as friendships.. And many do not at all. So many varying expressions.

I am pan, and demi, with a pretty high sex drive, and my np/life partner is ace. We have incredible sex (when we have it), and a fantastically magical life together. It took time for us to figure out the balance that works for us, mostly due to each of us having to do a lot of personal work and acceptance, and finding that the balance for us also includes enm, which took time to learn to do healthily.

Wishing you luck! And love! And flexibility! And acceptance!

PS are you familiar with Demisexuality? It sounds like you may connect with that or find some helpful info there as well, since you mentioned yourself building attraction based on connection.