Congrats on taking steps to improve your life! Future-you will thank you!
I will say, after 15 years of marriage and multiple (failed) attempts and losing & keeping the weight off --
this time is different and one of the biggest reasons is because my husband has also committed himself to a healthy lifestyle. I've lost weight in the past, and he was supportive in that he would encourage me...but he wasn't doing the same things so ultimately, it was just too easy for me to slip into old (bad) habits. Now...we keep each other in check - we still slip up - but we always tell each other now and we keep each other motivated.
My advice: get your fiance involved in a healthy lifestyle, too.