hey hope i get it rejection is a scary thing . i just dont think a letter is the way to go .it feels to me like something that would be done in middle school. wanting to ask someone out to coffee is a completely natural thing to want to do .i might be wrong but maybe your preoccupation with it here is that with your struggles this may seem like an awkward thing to do and are looking for acceptable ways to go about it to assure the best out come . like i said every one is a bit nervous when trying to get to know another person you might like better. its natural .so is asking him out for coffee.sending him a note to do it might be looked at by him as a bit strange, most people with the confidence will just ask in person hey i would love to get together with you for coffee sometime is this something that is possible . this would give him a chance to accept or decline.i bet if he declines it will have nothing to do with how you look.he doesnt seem like that kind of guy. if he is not interested then i am sure he will find a gentle and appropriate way to turn down the invitation . it could be he is already married,has a girlfriend,finds it unethical to go out with a customer from work .all of these could be reasons that are about him not you .