In Gordon MacDonald's book "Forging a Real World Faith" a particular chapter is enlightening for you, that is chapter six, "God is Multilingual." The main assertion is that "the conditions in which Christ-followers most naturally send and receive 'signals' to God are diverse, and we cannot make the mistake of prescribing any single way as best for all."
Each particular denomination has a certain style, culture, or tradition that worships or understands God in a slightly different way.
MacDonald identifies six instincts that Christians have to communicate, understand, and relate with God (I will list the general ideas of them below). I would advise you look especially at the Aesthetic Instinct, because this one is the most similar to Catholicism, and compare it with the other Instincts to see where you fit. If you like the tradition, incense, and atmosphere of Catholic or Orthodox churches, I would advise you convert, because then you will be closer to God, and worshiping and understanding him in a way that you most closely identify with.
However, if you are not Aesthetic but something else, I would advise you do not convert, because the tradition and atmosphere and repetition of Catholicism could end up driving you crazy or even pushing you further away from God if you are not connecting with him in the way that is easiest for you. Not every way is the same for everyone, so while your girlfriend may be Aesthetic, it would be foolish for you to convert if you were not as well (this is all assuming you know Catholic theology as well, such as things like the intercession of saints, and purgatory, and you have no problems with those kind of matters). I hope this helps. Do what brings you closer to God, not what brings you closer to your girlfriend. Keep in mind also that there are possibly other denominations that may be more appealing to you in relating to God.
Good luck, I hope this helps.
I. The Aesthetic Instinct (The agenda is majesty): "We are describing a person who seeks to be overwhelmed and impressed by the majesty and infinitude of God, and he most experiences it in the context of artistic and liturgical excellence ... the way things look and sound and connect is very, very important."
II. The Experiential Instinct (The agenda is joy): "I'm thinking of a Christ-follower who wants to 'feel' the presence of God when he meets him and to respond with the full range of emotions and even physical expression. Thus, an unaffected clapping of hands, stomping of feet, and even dancing singing and praying with unbridled enthusiasm, weeping and laughing."
III. The Activist Instinct (The agenda is achievement): "The activist sees all of Christ-following as service ... We're speaking of a person who is driven by compassion for the disadvantaged, or by prophetic anger against oppression ... he sees the world in desperate need of change, and he's committed to changing it."
IV. The Contemplative Instinct (The agenda is listening): "His instinct is to meet God not in the midst of a busy project but in the quiet of his inner life; that great space of the soul where one meditates, listens, and broods on the wordless whispers of a God who meets His people in solitude and silence."
V. The Student Instinct (The agenda is truth): "the student believes that God is the most profoundly discovered in Bible study ... out of this may flow a great theology, a framework for understanding as much as possible who God is and how He acts."
VI. The Relational Instinct (The agenda is love): "The relationalist is convinced that God is most present and intimate when people experience an unusual bonding together for fellowship or worship or mutual support ... the relationalist swims in people values."
