The realm of sin and forgiveness is confusing because, although Scripture doesn't specifically say so, it implies that there are two different realms. One is the on/off, binary realm of salvation. The other is the more nuanced realm of relationship.
Are all sins equal?
In regards to salvation, all sins are equal. James 2:10-11 explains, "For whoever keeps the whole law but fails in one point has become accountable for all of it. For he who said, 'Do not commit adultery,' also said, 'Do not murder.' If you do not commit adultery but do murder, you have become a transgressor of the law." Disobeying one part of the law puts us in a state of having transgressed the law. If we lie, we're not only guilty of lying, we're guilty of the law as a whole. Romans 6:23 explains that the appropriate punishment for sin—any sin—is death. This is an on/off, either/or situation. Either we are guilty of disobeying the law or we are not. Every single thought or action motivated by selfishness or greed or anger is as condemning as any other. Fortunately, Jesus forgives every sin (1 John 1:9).
God does distinguish between sins, however. When Moses saw the Israelites worshiping the golden calf, he declared, "You have sinned a great sin" (Exodus 32:30). And Jesus' reaction to the adulterous women He encountered (John 4:4-42; 8:1-11) was much different from how He interacted with the Pharisees (Matthew 3:7; 12:34; 23:33; Luke 3:7). He explains this in Matthew 23:23-24: "Woe to you, scribes and Pharisees, hypocrites! For you tithe mint and dill and cumin, and have neglected the weightier matters of the law: justice and mercy and faithfulness. These you ought to have done, without neglecting the others. You blind guides, straining out a gnat and swallowing a camel!"
We can also see a distinction in how God allows us to experience the earthly and relational repercussions of our sin. The desire for a friend's car may drive a wedge in a relationship, but not as much as the theft of that car. An angry thought may be quickly forgotten while murder leaves much deeper wounds. God's acknowledgement of this is seen in the laws He gave the Israelites. Transgressions had different punishments depending on how badly they injured relationships and the stability of Israel as a society.
Every sin condemns us equally, but every sin does not hurt others equally. Fortunately, God is more powerful than any sin. He can always forgive, and He can always heal relationships—with Himself and others.
The consequences of sin - What are they?
Does the Bible have a list of sins?
What are the seven deadly sins?
How can I know what is a sin and what isn't?
Is there an unpardonable sin? What is it?
Truth about Sin