confused

My fiance and I have been together for almost two years and are going to be getting married this year. He gets jealous over the most stupid things like ..........oh that guy from work talked to you? Thought you said you dont talk to him?........ When I only talk to that person about work and thats it. And just because he starts a converstation with me its my fault? I dont know what to do to fix this. And another thing if I spend money doesnt matter how much he gets pissy for me wasting money on crap we dont need. And then will ingrone me because he is mad and will throw the crap away that I bought for him that I wasted money on. I am very confused. I love this man like crazy and he means the world to me and when we are not arguing everything is perfect. I just want him to mellow out. Is that ever going to happen? Any tips on keeping him happy when the difficult times come along?