What's the next step? Move in together and not pay any of the rent?

Yeah, basically. In my case:

• In-laws provided us with a rent-free place to live (their basement).
• In-laws paid all tuition fees for my wife.
• In-laws paid for a relatively lavish wedding.
• In-laws generously helped with the down-payment on our current place.
• In-laws frequently give us stuff.

While I don't mind, and in fact prefer, being bossed around by my wife - even I sometimes resent the degree of influence my in-laws have on our life. I can imagine that for someone less docile or more proud this would be a source of conflict.

I am passionately in love with my wife and have been since she first kissed me. I did not have to face the situation where an affluent girl has a crush on me and I'm not that into her - I wouldn't want to make any particular recommendations for that situation :)