What does 一起 imply about a romantic relationship? In stories I see 一起 used to describe a romantic couple being "together", but I would like to understand what it implies.

For example: “……要是我能和她在一起该多好啊！” in this context the boy has just seen a very pretty girl. Does he want to meet her? Date her? Live with her? Marry her? Have sex with her?

Later: “再说，他们俩已经在一起了……怕是不会再嫁给别人了。” in this context, they have been sleeping together, and the speaker clearly means to imply the girl can't be married to anyone else now.

I understand context is always a factor, but I want to understand the more open-ended cases like the first one where characters wish to be or talk about being "在一起" and what sort of relationship is implied.
在一起 (be together) is a subtle way to say "做情侶" (be lovers/ a couple) 

be boyfriend and girlfriend, common law partners or husband and wife

just like 喜歡 (like) is a more subtle way to say 愛 (love) 

Most Chinese are quite reserved, words like 做情侶 (be lovers) or 愛(love) are rarely used directly