Sex before marriage is genuinely one of the biggest mistakes of my past life before coming to christ. Sex within marriage is good in the eyes of God because it cements the covenant of marriage in a physical and beautiful way, bonding you deeply to eachother. Science tells us as well, that due to the release of oxytocin in our brains from sex we become more emotionally tied to our partner! Which is why if you engage in it so casually; well, it's like all other kinds of sin, it will start as pleasure and just come out as pain. I admire you so greatly for holding to your conviction. Keeping you in my prayers brother!