HELP , please i dont understand this?

i like this guys alot ive been talking to hime for over a year , but i was in georgia i finnaly moved back and i hungout with him ( weve hungout more then 10 time & sometimes we'd just drive and talk )first it was just sopossed to be sex atleast thats what i thought , then i relized he wanted more all of a sudden i dont even get it but he was saying he loved me , then we got together the night agter and he said he's never felt this way before he constanty tell me he loves me while intercourse i tell him it back . the other day we where lyying in his bed , and i have my dads promise ring on my left ring finger he take it off and walks into his closet he come out and says try this on i slipped it on my my left ring finger . that night when he was driving me home he told me this could be our promise ring ithe night after we where lying in bed and we where talking about how he's going to the army in 4 days & he's like ill wait for you ,if you can wait for me im reall young i dont think i can go 5 years without sex witch seems real bad but he said he can visit me when he gets to go home but he took the ring off got on his knees and said kayla will you marry me i said yess , he's always talking about how when he's out of the army ill be out of highschool and we will get married . this seems like its too good to be true . i guess i have reallllly big feelings for this guy , fbut ttheres a 5 yrs difference but im very mature for my age , i dont know what to do .