The Lord will forgive the truly repentant sinner.
However, it is on us to be "truly repentant"... and not just offer lip service, like kids who are forced to say "sorry" to someone they hurt.
They begrudgingly mumble the words, but, it is not from the heart.
Therefore, while the Lord forgives, we must truly repent, and then also forgive ourselves, and redouble our efforts to not repeat that sin.
We should not count on God's forgiveness... because that opens the way for us to think we can sin right now, because God will forgive us when we take a moment to think of Him and ask His forgiveness. We can become callous. Therein lies the problem.
When we ask for the intercession of others, or through the prayers of the Holy Mother of God, saints, etc.... It is not that God would not have heard us when we spoke to Him... but... we ask them, who are already in "good standing" to intercede for us...
If a father has two sons, and one is always the good boy, while the other is always getting into trouble... when the naughty boy borrows dad's car without permission, and then dents it, he runs to his "good" brother and asks him to tell dad how sorry he is. The brother finds the father and kindly diffuses the situation, "hey dad, Joey realizes he made a mistake when he took your car, and he promises to pay you for the damages..." even before the father realizes the other one has sinned against him, this brother has explained the situation.
When we ask for the Theotokos to intercede... the Lord respects and loves His mother... even turning water into wine, before it was His time... only because she asked it of Him. Therefore, we often ask for her to intercede on our behalf... because she was/is fully human, and as a mother has compassion upon us, her children, like nobody else...so we ask her to help us.
God will always hear YOU... you do not NEED to go through saints... but, sometimes it helps us, and calms us, knowing that not only are "we" asking for His forgiveness for Sins a, b, and c... but, someone else is also asking Him to forgive us.