There is no difference between Christians and Roman Catholics in terms of the Christian Faith....Roman Catholicism is known as a Denomination of Christianity, just like Baptist, Methodist, Anglican...etc.
Unless you are the Monarch of England, you are permitted by any Denomination to marry someone of a different Denomination.
However, there are differences between the denominations. Roman Catholics are High Church...so they will enjoy pomp, ritual, sung litergy, sung literny, a very formal setting of Holy Communion...and they will NOT allow YOU to receive Communion at their Churches UNLESS you become a member of that denomination via Baptism or Confirmation.
The Roman Church runs under the authority of The Roman Curia...a Council based in The Vatican City and headed by The Bishop of Rome, also known as "The Pope" or "Pontifex Maximus"
The Roman Church is run on a local basis in an Episcopal Manner, that means each area is split into Diocese, headed by a Bishop, above him an Archbishop, and above him a Cardinal. Cardinals are known as "Princes of The Church" and many have positions within the Curia itself...they meet together to decide which one of them should be Bishop of Rome when a Pope dies or resigns.
Inside the Roman Tradition there are certain societies, and it IS very important that if you do get involved with a Roman Catholic, you find out if he is a member of any religious, or monastic society...there are many, and they originated from times when the Church ran its Monastic programmes...they are what remains of the Roman Catholic Mystics and Contemplatives...the most famous are the Jesuits, the Benedictines, and the Augustinians...If your man turns out to be one of them, then get back to me and I can provide more detail on that particular society.
Remember...it also matters how devote he is...he might call himself Catholic...but does he actually follow the Popes advice, or like many Romans...simply ignore what the Pope says?
Questions to ask include...does he accept forms of contraceptive...because in theory Catholics shouldnt...but most do.
How Marian is he..? What is his Views on Mary? Was she without sin? Was she assumpted or did she die?
Does he ask the saints for intercessions? Does he wear a medalion with a saint on it?
Does he believe in Transubstantiation? What are his views on Vatican Two?
Like with Anglicanism...there is room for a great many levels in one denomination.
I dont think, ultimately, you would get along theologically with someone VERY Roman. But someone who was at the low church end of Romanism, you might be able to tollerate.