The following is an adapted response to someone who asked whether I thought they could change. I’ve edited my response to remove any personal references including any allusions to the nature of the issue.
I do think you can change. I can’t guarantee that. But change is always possible through the cross, the word and the Holy Spirit.
I would encourage you to explore with someone the underlying reasons for your behaviour. Think of your behaviour as a symptom and then explore the cause. Your behaviour will have met some desire, some ‘need’. Then you can explore how the gospel more fully and more truly meets that desire. That in itself will not bring change, but it will highlight where the battle is truly to be fought. You will then need someone who holds you accountable and encourages in that fight, who speaks the truth of the gospel to you.
You say that you are not an awful person. I am sure it is true that you are no more awful than other people, myself included. But this may be an opportunity for you to face up to how pervasive and extensive sin is in your life (as it is in the life of anyone). Remember that even our righteous acts are often motivated by sinful and selfish reasons (the desire to prove ourselves, the fear of others, the need to be in control and so on). Don’t just look at the bad things you have done; look at the good things you have done for bad reasons. That won’t be fun. But it will lead to a greater appreciation of grace and appreciating grace is the engine of change. It may also help you identify some of the underlying reasons for your behaviour (you may find that what led to your behaviour was also what motivated your good works). You may find yourself in a place where you have nothing to offer and depend entirely on God’s grace – and that is a good place to be and the only honest place to be!
I would suggest your primary responsibility is twofold. First, to guard your own heart (Proverbs 4:23) – both to explore the underlying issues, but also to guard against bitterness and resentment. Work hard at finding your joy in Christ. Read the Scriptures every day, remind yourself of the gospel, pray for the Holy Spirit’s work – all until you feel your heart moved each day with love, fear, joy, hope, faith, conviction, confession, wonder and so on. Do this day by day – one day’s neglect will be a step towards a hardening of your heart (Hebrews 3:12-13).
Second, serve other people. Put their needs before your own; put their emotional needs before your own. This will be a tough call for you. But it is the right thing to do and I suspect will also be good for you. Serving others takes us out of ourselves and puts us in the path of christlike living.