Please speak to them. I promise you, if they are a worthy person they will support you.
I told my guy something last night that I was super anxious about (following on from Asking FWB for TLC) and his response: you don’t have to worry you fine girl. We can go at whatever pace you want and make sure you are comfortable 
I cried. I fucking cried because for the first time ever a male partner RESPECTED MY BOUNDARY. My trust in him has just multiplied and he is even sexier rn (I did not think that was possible).