I'm at an impasse currently. I once had a horse in a previous incarnation who was great, never gave me any trouble and had my back through Elder Scrolls IV. Now I am trying to figure out if it is possible to get Shadowmere after receiving the ability to summon a DG mount? (I'm sorry if there were any spoilers or if it was too vague) I'd really appreciate any opinions on the subject, including whether I should have posted this in the other forum I just really didn't want to know anything about Skyrim or Dawnguard before I had played it! Thank you so much!

The DG mount is a summon. You can have him and a horse.