My Girlfriend lives a double life? am i dumb for being with her or is my love for her just that strong?

ive ben with her for 8 going on to nine years now, i have no idea when she started but this is it in a nutshell, she says she loves me right, yet she has numerous men online that are in a well kind of like virtual relationship with her, she sends them naked pictures and everything, has even given them her adress and real name, she tells me that its okay because shes with me in the real, but 1 incodent happened a few months back, i went out to play at a gig one night, i get home from the gig felling really good, but something was bothering me, i couldnt help it so i checked her fone and there were messages on there telling her to meet this individual, and i read on, and the messages just ended up pissing me off, she fucked this person who ever she met, while i was out giging, i have ben a loyal man to her for all these years, not once did i falter in my loyalty, so shes asleep right, i wake her up, and ask her what she got up to, and she replies with, "not much just stayed home waiting for you" and then i ask her if shes loyal to me, she then replies with,"so you read the messages on my fone huh?", i said yes and asked her "why?", she then goes on and tells me she was bored?, i asked her earlier if she wanted to come to the gig and she said no, but yeh that was that, we sorted things out i forgave her and all (as i always do),she promised me shed never do it again, but this was the first time i ever caught her, my instincts were telling me and i took to my instincts were right, so later on down the track i have those same feelings so i check her fone while shes asleep, turns out she had been wanting to meet another man?, so i just let that one slide and see what happens, this time she didnt fuck this person she just met with him and had dinner with him, i didnt think nothing of it, now ive confronted her about these things and she just tells me that, thats the way she always will be and i either accept her as she is or i leave her, now i love this woman with all my heart, and i really want to marry her, she has alot more men on her fone that she is having virtual relationships with and i have been trying my hardest to snap her out of it, but she wont budge, she calls other people fake and considers herself a real person, bitch please???, oooh i guess im just too weak to leave her because i love her too much somebody please help me with this woman problem, weve tried breaking up many times but we keep running back to eachother for some reason??