What type of love interest they would be?
A soft, slow-burn love interest. He'll fall quietly and deeply before you know it, but not just with anybody. If you can prove that you'll stick with him, that might be enough to breach his walls.
Their dynamic and personality to the friend group?
He's the emotional support in a group. Sure, he gets teased for his soft voice and calm energy, but that's exactly what gets people to be around him.
What they would bring to the story?
He'd add emotional depth, vulnerability, warmth and realism. Guys can be soft, and I think he'd be a great way to represent that.