actually i think in some cases 爱人 could be interchangeable with 情人 or 恋人 though often not。。In my society, 爱人 is just the meaning of "spouse". If one want to say lover, the 情人 is the right term. For "husband" , I give your an order by frequency: 她老公(hubby) 她男人(her man) 她爱人(beloved) 她丈夫(husband). For "wife", the order is : 他老婆(?) 他媳妇(housewife? not sure) 他爱人(beloved) 他妻子(wife)。
Well, I think it's a very common term in the daily talks in mainland China, but since I've never been to China, and I learned that many people say this in their daily talks only from movies and TV operas, I am unable to assert it's not your situation.Don't worry, both are correct. what cochon said is right. it is not a very useful word, because chinese people aren't used to say that, like: lover, dear, darling... except on letters, or poems.
Yes, IMHO, 媳妇 means wife in North China, and means daughter-in-laws in South China.Over here, only daughter-in-laws are addressed as 媳妇. So there is a regional difference in this aspect.
At least, in HuNan province, 爱人 is the same as "spouse", where it means no romantic thing.well, it is also used in very romantic and/or private situations. because chinese people are usually fairy shy. by the way, I'm chinese.