serious about (someone)
Wanting or committed to a permanent or long-term romantic relationship with one. I know he's getting really serious about her. I wouldn't be surprised if he proposed in the next year or two. I don't really want to get serious about anyone during my time in college. I'd rather be free to do as I please.
serious about someone
in love with someone; romantically interested in someone. I'm afraid I'm getting serious about Bill. Bill, unfortunately, is pretty serious about Mary.
serious about someone
mod. in love, or almost in love, with someone. I’m afraid I’m getting serious about Bill.