This is a bold step 'fessing up to this. It normally goes unspoken and the person (if they think it is wrong) lives with a ton of guilt and condemnation.
The bible is relatively (not completely) silent on the subject which in one sense is kind of amazing since in the Law of Moses every kind of aberrant sexual behavior is denounced but no mention of "M." And couple that with the fact that male M played a big part in the religious celebrations of at least one of the Egyptian "gods" and it is depicted in numerous hieroglyphs. It was clearly known and understood well.
There is the whole "unclean until sundown" for wet dreams and regular sex, but Tamay (unclean) is NOT sin, or else normal marital relations would be sinful and so would be a women's monthly cycle and childbirth.
The one place I believe scripture mentions it (and in a positive way) is in the Song of Solomon chapter 5 starting in verse 2. And it is Shulamite who is doing it.
[brief hint to get you thru the symbolism:
garden/flowers/lilies = female genitals
frankincense/myrrh = aroused female wetness]
SoS 5.2a I was asleep but my heart was awake.
A dream or fantasy
SoS 5.4 My beloved extended his hand through the opening, [literally "by the hole"]
And my feelings were aroused for him.
Many translations add "door" to the text which is not in there at all.
SoS 5.5 I arose to open to my beloved;
And my hands dripped with myrrh,
And my fingers with liquid myrrh,
On the handles of the bolt.
"liquid" = flowing out or passing. all over her hands.
I think you get the picture. I have probably gotten too graphic already.
For these reasons I do not believe M in and of itself is inherently sinful. (my opinion based on the above)
That said, if it is coupled with porn or excessive or specific fantasizing CAN be sinful. I would consider that to be like coveting or idolizing someone for personal gratification. To avoid the sinful part one could concentrate only on the physical feelings. (again - my opinion)
I take it from what you said about deleting "stories" etc that you have decided to stop? If you are convinced God is calling you to quit; absolutely go for it. But make sure it is God and NOT the devil's condemnation (he tries to fake God's voice) or a personal sense of guilt.
Go slow. Don't beat yourself up if you slip up.
If you are giving up cigarettes, you start increasing the time between smokes. If you smoke every hour, stretch it out to every 2 hours for several days. When you are starting to get used to that frequency then cut it to every 4 hours for a few more days. (at that point you have already decreased your smokes by 75%)
I would suggest a similar strategy. Going "cold turkey" with smokes, narcotics, alcohol etc. usually ends in failure. It will with this as well.
Be sure to pray a LOT, read the bible a LOT, keep close to christian friends a LOT; and having an accountability partner to be able to call at 3 am when it feels like you are dying is good as well.
Our Lord's Peace to you my sister!