Why does my girlfriend act like this if she's really in love with me?

my gf says shes in love w me and theres no1 else but we dnt spend much time 2gether. we work diff., shifts she says when i come home and lay bside her thats spendin time 2gether...i dnt agree. when shes around ppl she changes her attitude. we get along when we're 2gether but when we're apart i feel like shes doin sumthen she shudnt be...she says im tripn and i need 2 stop. am i? ive been depressed here lately shud i try 2 trust her? shes left me twice 4 her ex and she came bk 2 me bc she said she ***** stand being away from me. but since shes bn back, thats when we argue more...is it insecurity? shud i just stop and act like i dnt care about what she does...please give me an answer...