it is up to individual choice, SGGS is more concerned with you, than what you eat
There are some branches of Sikhism that believe it to be, Nihangs for one
You have not done anything for God to forgive, however God may help you forgive yourself 
I too have a lover, I am unwed, I am mona, I eat meat, and I had a murky past right up until age 40. I am also a Sikh.
Sikhism is not a magic club where entry is only for the good and pious, Sikhism is a way of life where you slowly integrate your life into it, and day by day, live by the will of the Guru, rather than your own will. You carry forward all that is Gurmukh. Having a lover is not a problem, provided she is not married to someone else. Sikhism is more concerned with your thoughts and actions, rather than who you sleep with or what you eat
