If this is something you'd truly like to work on, not out of a sense of guilt but because you would enjoy occasionally reciprocating, there are a wealth of resources out there for the enthusiastic amateur (you are far from the only would-be blow-jobber whose spirit is willing but gag reflex is weak). You have more options than "no blow jobs, ever" and "regular whole-hog sessions to completion that result in vomiting."

Some people give gifts in order to bewilder, confuse, and manipulate their recipients.

Reciprocating oral sex is, in general, a very good idea!

Some struggling marriages can be salvaged with hard work and counseling; others should be dismantled and stripped for parts.

As you feel increasingly comfortable around your friends, I think it's more than fine to share the basic details of your heroin addiction with them. If they seem receptive, you can feel free to talk about it in further detail; if they seem judgmental or uncomfortable, you can move on to other topics.

Knowledge of death is the beginning of wisdom.

I'm pretty sure there's no sexuality that justifies constant low-level harassment.