Desperately need your help

In brief , I overstayed my visa by 2 years and I have been working illegally.
I have now stopped working.Moreover , I have been living with my girlfriend who is a french national for around 3 years and now we are deciding to get married abroad in south africa during the summer time.

I just want to know the following :

1. what sort of questions will the bia asked me when exiting the country

2. To what extent working illegally will affect my chance of getting a spouse visa

Thanks a lot for your help