If I love her and I love you, could you love her too?

It all depends on the logistics, lady.

Although, my capacity to love is rather elastic, so perhaps I'll surprise us both.

maybe, but that isn't a given that just because you like both of us we'd like each other.

Been there, done that. It can be wonderful.

What is in it for me to love you both?

I can sure try 🙃

isn't that the transitive quality in mathematics?

Love is not a transitive property, afaik

Maybe. I'd hang out and get to know her to find out. I'd really adore love like that.