Taking the train from FRA to Trier, and thought wife and I would stay onvernight in one town along the way. Any suggestions on a romantic hotel and town to stay at in May?

http://www.bellevue-hotel.de/

if you like art deco and a fine view

I'd suggest Koblenz - you have to change trains there anyway.

You don't "have" to change in Koblenz - there are trains that change in Saarbrucken and another in Mannheim. But that doesn't mean you should stay in either of those places or other stops along those routes.

Koblenz is a city and although it has a certain charm in a limited area, I think you would find someplace like Cochem to be far more romantic. Cochem is on the direct rail route to Trier and on one of the faster routes.

Although I don't like the Rhine - too much rail and barge traffic - two other places that have aficionados are Riudesheim and St. Goarshausen, also on the rail route but on slower trains.

Schloss Belvedere is in a town not on the direct rail line, but reachable by a regional connection from the stop after Cochem (Bullay) in about 20 minutes.

I don't have a personal recommendation on a romantic hotel in Cochem, perhaps others will know of something in the town area?

We biked up the Rhine and down the Mosel in 2011 to Trier. Bernkastel was a favourite town to stay in, with lots of places to eat and shops to visit.

Stayed here:http://www.tripadvisor.ca/Hotel_Revi...alatinate.html
And were treated very well.