Firstly, welcome back!
This question is extremely pastoral in nature, and as questions of this nature, should be directed towards said person’s pastor. However, those experiencing homosexual attractions (or SSA) are called to live chaste lives. This civil union is contrary to that chastity that they are called to.
I will refrain from going into more specifics since this should be directed towards said person’s pastor in a private setting to discuss the possibility of going through RCIA.