To the OP:
You are welcome to participate in the Mass, to explore Catholicism through RCIA and other means, and to become involved in the life of a parish, to some extent, prior to joining the Church.
There are four distinct “periods” of the RCIA (Rite of Christian Initiation of Adults) process – the first being the “inquiry” stage. You will work on recognizing how God is at work in your life. For you to proceed formally to the next period, the period of formal catechesis, you would need to discern if you are truly ready to work on converting in mind, heart and will in your relationship with Jesus and His Church. You would need to discern your desire to turn away from sin and to develop a desire for virtue. You would need to yearn for a solid understanding of the Gospel as revealed by Christ and as passed down from the apostolic age through the Church He founded. You would accept that you want to live a Catholic lifestyle – which means more than an intellectual understanding of the teachings and more than attending Mass every Sunday – it means changing your lifestyle. It means trusting that God with His grace will help you in your journey of understanding, accepting and living the faith.
Catechesis continues during the third period of the RCIA, the period of Purification and Enlightenment, but there is more intense spiritual conversion work going on.
The fourth RCIA period, Mystagogy, is the one-year period beginning upon the reception into the Church when the sacraments of initiation are received.
When becoming Catholic, you will profess that you believe all that the Catholic Church “believes, teaches, and proclaims to be revealed by God.” Acknowledging that any sexual activity outside of marriage (between a man and a woman) is a mortal sin would be part of your particular lifestyle change. To avoid the near occasion of sin, you would need to move away from the woman you currently have a lesbian relationship with. If you truly love God, you would care about her soul too, not just yours. That would be a greater act of friendship, of love, from you to her than any sexual activity you and she share. If you believe you cannot commit to refraining from any sexual activity outside of marriage, then you would not yet be ready to be received into the Church.
I will remember you in my prayers.
**from the U.S. Bishops’ Pastoral Letter on Marriage (November 2009):
…The differences between male and female are complementary. Male and female are distinct bodily ways of being human, of being open to God and to one another—two distinct yet harmonizing ways of responding to the vocation to love…
…The Church upholds the human dignity of homosexual persons, who are to “be accepted
with respect, compassion, and sensitivity.” She also encourages all persons to have chaste friendships. “Chastity is expressed notably in friendship with one’s neighbor. Whether it develops between persons of the same or opposite sex, friendship represents a great good for all.”
At the same time, the Church teaches that homosexual acts “are contrary to the natural
law. They close the sexual act to the gift of life. They do not proceed from a genuine affective and sexual complementarity. Under no circumstances can they be approved.”**
usccb.org/meetings/2009Fall/docs/Marriage_Love_Life_pastoral_letter.pdf