Confessing to Girlfriend

Hello all,

I’m preparing to propose to my girlfriend here in the next month and need some personal help and advice.

I am a convert to the church and have been a member for about 3 years now. Before I was a member I ended up having premarital sex(because I wasn’t a member and law of Chasity wasn’t a thing to me)

I am wanting to tell these things to my girlfriend because I feel she deserves to know if we are going to get married and sealed. But it is absolutely killing me inside thinking about hurting her like this. Maybe I should talk with my bishop for help? What are your thoughts?