Wtf am i overreacting ?

I don't know what to think is he planning on cheating ?

Rewind: we have been together 5 years now i really thought we are good together.yes we have arguments like any normal couple but we get through it and we have complete trust of each other but I found this messege on his messenger.

Ur excuse me but your supposed to be engaged to me. I asked him if he was happy with me and still wanted to be with me which he replied "yes course I do" it was only a month ago he sent me this messege....

Is he planning on cheating ? I feel I'm only here for him untill this "other woman" takes him away.why would he even say that if he truly does love me as much as he says he does ? I really don't know what to do or think

EDIT: without knowing the truth yet and im not defending his ass but...I am hoping it's innocent. I don't think he has cheated on me yet(obviously I dont want him to either) he's always at work or with me he doesnt really go out much not long enough to meet up with someone. I have this fear he does like her. But he has known her many years ( im hoping its more of a crush then actual wanting to be with her) He is the kind of man to call everyone darling and sweetheart and put kisses on end of messeges,men or women I don't have a problem with that he's always done that. We have been through hell of alot together, (he was a drug addict) I helped get him clean and even tho he had a few relapses is now clean and tells me or anyone that will listen I saved his life. I constantly get messeges with soppy gifs and messeges like above. I'm his baby and get told he loves me hundreds of times a day. Hes done that way before we officially got together.This Is why I'm finding it so difficult to get my head around. I really don't think he would cheat on me. I'm going to talk to him when he gets home from work. I need the truth from him.i can't live with him knowing that one day I won't be good enough anymore.