How should I know if you’re living in mortal sin? I’m not God, and neither is anyone else here!
I do know that God DOES listen to the prayers of ALL His people, and that includes sinners. And I do know about Jesus’ parable of the Pharisee and the publican. From what I gathered about that parable, I think God was a little more favorably impressed with the publican’s attitude.
I also know that if I really love a fellow creature, I hurry to address the needs of that relationship. Same with God, not that He has any real needs, because He’s God! But I have a need to try to get my relationship with Him “right,” and that is why my conscience bothers me when I encounter such qualms.
That’s why the Sacrament of Reconciliation. And if there is something that I really am too attached to that I’m NOT willing to let go at this time, I ask God to MAKE me willing!
He usually does this, in all sorts of ways. That’s the funny thing about mortal sin. Not only is it a grave offense against God, but the sins in question usually result in consequences that really aren’t even in our own temporal best interests. Sin might LOOK like fun at first, but it usually doesn’t play out very well, even here on earth.
For example, say someone likes gossip and calumny, and takes that into the workplace with them. As mortal sins go, that’s a pretty “tame” one (by that I mean it’s not something like murder or adultery, not that “dramatic” a mortal sin, I mean, so let’s use that as an example.) They may undermine a rival at first. But their coworkers get wise to them, they get a reputation as a gossiper and liar, and they sooner or later lose all credibility, and take themselves out of the running for, for example, promotion. Or they may just be effectively ostracized by their colleagues. Forty hours a week of being ostracized because one was acting like a jerk is a lot of time out of one’s life. See what I mean?
Obviously, I don’t know what particular brand of mortal sin you’re talking about, but you might want to ask yourself how, in addition to offending God, you’re shooting yourself in the foot, and guaranteeing some misery for yourself right here on earth. That might be enough to make you willing to make some changes. God will certainly forgive our sins, but He does expect us to give it a real try to keep ourselves in a state of grace. And He does give us the resources to do that, if we are willing to at least be willing to try!