Can a liar ever truly change if they are trying, (lies of past).

I have posted here before about my fiancé lying to me about his sexual past. He had told me he slept with two girls, but I met a girl by chance who told me she was also with him, and he then admitted he had been lying for 2-3 years and actually there were 10 girls he slept with and not 2. He made me feel guilty about the one guy I slept with because he was jealous. Throughout the relationship I had asked him 100-200 times about his past due to my own jealousy and he stuck to his story. Now that the truth is out, he is so willing to change, he is seeking therapy, couples therapy, he is ridding himself of ego etc. He is distraught and doesn’t want to lose us, but I am concerned if a liar can truly change? Will he just lie again to cover up any difficult truths? I also am concerned about one day marrying him and not being able to fully forgive for the lies and see him a a new man. I want to feel joy on my wedding day and look at a man I respect. I love him truly. Thank you kind souls!