If you want to get into relative grades of sin, I think that "monogamous" lesbianism is better than the promiscuity which typifies male homosexuality or the swinging promiscuous hetero lifestyle. God's desire is love, which requires commitment, "for better or worse."
All sin is founded on rebellion to God. Therefore, in that sense, all sin is equivalent. But as far as how sinful behavior and actions manifest themselves, all sins are not equal nor do they have the same effect on the sinner or those around him or her.
It’s a long topic and I don’t have time to do it justice, but just as all physical ailments are not the same (hangnail, sunburn, measles, AIDs, cancer...), similarly the spiritual sickness of sin is a continuum.