This is the first time I have seen you speak not so smoothly. It may be because I sit next to you and you are nervous, or it may be because this thing is very desirable for you, so you are serious.
This is the first time I've seen you speak less fluently, maybe because I'm sitting next to you and you're nervous, maybe it's because it's something you'd love to get, so you're serious
This is the first time I see you speak not so fluently. Maybe it's because I'm sitting next to you and you're nervous, or maybe it's because you want to get it, so you're serious