Is it forbidden to have sex or masturbate when your fasting in Christianity ?

I can't speak for all Christian faiths.

Catholicism, you are always called to chastity, meaning that unless you are married you should not be having sexual relations ever. If you are married, there are not times when you are asked to abstain from sexual relations. It's an accepted and essential part of the marital relationship. Kissing and hugging are acceptable outside of marriage but oral sex, intercourse and manual sexual stimulation are not considered acceptable at any time. I believe this is also true of the Jewish faith and most other Christian faiths.

Fasting in the Catholic faith relates only to food. It used to be that Catholics abstained from eating meat on Wednesdays and Fridays. Then it was reduced to just Fridays. Now we just abstain from eating meat on Friday's during lent. Some more strict Catholics abstain from eating meat every Friday. I abstain from eating meat every Friday just to remind myself of Jesus sacrifice. It is not a huge sacrifice on my part because I enjoy the other dishes I eat just as much, but the habit makes me more mindful of my faith, and so I find it worthwhile to do year-round.

It used to be, also, that Catholics fasted from all food and beverages from midnight every Saturday until they received communion. This is part of why brunch and big mid-day Sunday family dinners became such a big deal - people were really hungry after missing breakfast, so would have a large meal right after church. This is no longer considered a requirement, though some strict Catholics still observe it. I don't observe this tradition because I'm pre-diabetic and I get too weak and shaky when I don't eat breakfast. Otherwise, I probably would.

I don't know of Christian faiths other than Catholicism having any form of fasting among their religious traditions. Can anyone else provide information on that?

In any event, no - fasting does not pertain to sexual relations within a marriage.

Hi I have a friend that was a JW and she had sex outside of marriage the elders got news of this and she was decomisioned from there religin of this act and her family is in this religin and she isn't alowd contact witch I think is a load of crap as I wouldn't think god would outcast his childeren that he has created. I'm no Christian and life started with adam an eve. WERE THEY MARRIED AND WHO MARRIED THEM BEFORE HAVING A CHILD?