The gap which has appeared between your teeth is due to not using your retainers as prescribed. You should have kept using the retainers as long as your dentist
suggested. Secondly the gap between your teeth is not due to tobacco but due to the relapse ,as the teeth which were moved by orthodontic treatment are going back to their original position. Needless to say, you will have to quit tobacco
abuse and secondly since you are about to get married the best option in your case to fill the gaps would be to use invisible aligners, which can take care of gaps in the best possible way .if possible and if you have time then you may go for conventional orthodontic treatment with braces. It will also take care of your problem but this time do not forget to wear retainers as prescribed. It should take less time this time ,Since only gaps are there between your teeth. So consult a orthodontist and let him decide whatever is best for you .all the best.