What does it mean to "grieve the Holy Spirit"?
Here is the good news: First John 1:9 says that when we confess our sins, He is faithful to forgive us.
Grieving the Holy Spirit (mentioned in Ephesians 4:30) is when you disobey the Word of God. You know what the Word of God says, but you don't want to do it. The Holy Spirit is the Spirit of Truth, so if you habitually lie, you grieve the Holy Spirit. He is the Spirit of peace, so if you habitually create strife, you grieve the Holy Spirit.
Here is the good news: First John 1:9 says that when we confess our sins, He is faithful to forgive us. If I'm driving on the highway and I miss my exit, I don't keep heading in the wrong direction, saying, "Oh no, I missed my exit!" Rather, I get off at the next exit, turn around, and return to the correct road I'm supposed to travel. And that's exactly what it means to confess. Change directions. Yield to the Spirit. Ask Him to fill you, to pull you in His direction, to guide you on His road.
As you do this, He will fill you. He will make you conscious of the presence of the Lord Jesus. He will guide you with His Word. His thoughts will become your thoughts. His standards will become your standards. His work will become your work. And you will find fulfillment and purpose in life.