Mariella does "a little dance," and jumps delicately into an issue that she sees no avoidance of and no working around, now.
.
"Alex, I know we've been flirting for a while now.. and I do flirt with a lot of guys, but I don't understand it.  With you.. I can't tell if you're serious or not."

She gives a questioning look, almost a pleading but in suspense.  Alex looks reflective – not so much coldly so, but almost afflicted.   He then decisively sits down next to her – closely next to her – and puts an arm around her.  Mariella seems shifty, but accepts it.  Alex looks at her directly.

"Mariella... I like you.  When I talk to you, I have to flirt.  I couldn't possibly do otherwise and still feel...alive. Because I do love you.  And I want you not just because you're a pretty woman, but for everything you are."

"But, you're not... the one."

Mariella doesn't seem to know how to take this, to Alex's own bemusement.  Alex quickly searches for a better way of putting it.

"Look, I know what women are after... and I just don't want to break your heart.  I want to tell you how it is."

Mariella then proceeds to give him an interesting and graceful, if not entirely innocent, speech about how life's too short, and if you'll settle for nothing but perfection in this world, you're just that more likely to get...nothing.

What happens next, she couldn't have anticipated.  Immediately Alex's eyes light up like flint sparks, he hugs her close and nuzzles his face against hers.. he sighs in relief and gives her a long, soft kiss on the cheek.  With *both* arms around her and still nuzzled against her face, he asks – viscerally and unthinkingly –, "Do you really mean that?"