gonna = 'going to'. It's much more informal. Therefore, this sentence can be understood as 'Nothing's going to change my love for you' (我對你的愛是沒有東西可改變的!)
'Nothing is going to change my love for you' means that no matter what happens in life, my love for you will remain the same. This is a romantic way to express your feelings to someone, just like saying 'I love you' but it's more like a promise.
Nothing can change the way this person feels about you, what even happens in the future, the love will not change. He loves you now, he will love you ever and ever.