I hope that you'll be in safe hands
The right guy will be patient, taking the time to put you at ease and to nicely caress your ass to get you in the mood. I can recommend having several sessions, leading up to the main event, of gentle fingering & using slim toys - gradually less gentle, as you become more brave. When you're finally ready, it helps to first tease yourself with the warm jet from a shower-head (or share a shower for him to do it to you) to relax your ass, not to mention cleanse your ass. So, have fun loving your bum.