Is it cheating?

Can someone please explain to me, because I am very confused at this point. Why would a guy who is in a relationship look at pictures of other girls to "get off"? We have a regular sex life, but there are times when we are not together during the day, so he does it himself. It's not even porn (though sometimes that too), just Facebook pictures of other girls. There's one in particular he looks at quite often, she is on his friendlist and I suppose she's an ex of his. He hasn't contacted her, but him looking at her profile means he thinks about her, obviously. He once said he met an ex of his on the bus some weeks ago and they talked, so I'm thinking it was her. We've talked about his actions and he's even said it's a fetish of his, that he's done the same in previous relationships aswell and doesn't plan on stopping, because it "doesn't mean anything", meaning it doesn't change our relationship. He said that's normal for him and I shouldn't worry, but I still do. IS it normal? When I offered him pictures of myself, he did like them, but still kept on doing the same. He's said he "needs diversity", hah.. Yes, those girls are bustier than I am and he admits he likes breasts a lot. I've told him how thia situation makes me feel and basically the conclusion was that I need to get over it and stop trying to control his actions. I have considered getting a boob job and he has said he would "definitely like me more" then. I'd just be devastated if doing so wouldn't change his habits. I understand that I probably shouldn't have looked at his profile in the first place. After I "check" on his browsing history and see the same thing once again, I feel helpless and hurt (again). I know that I shouldn't do that, because it means invading his privacy and is a bad thing to do anyway. It impacts me to the point that I don't feel like he "deserves" to have sex with me at the end of the day when I know what he's been doing by himself, but I give in anyway and the loop continues. I do love him and find it hard to accept that he sees other women, especially those he knows in real life, sexually attractive. That just doesn't sit right with me, because on some level I feel that's cheating. I've asked him if that means he wouldn't mind doing it with them in real life, and he didn't deny it. We have talked about having a foursome, I'm just thinking he wants to have sex with other women. Would he be satisfied for once then, or would he want to explore more?.. I don't know what to do, because nothing has changed about this situation. He is a good guy overall, this is the only thing that's bothering me. Breaking up is not an option; should I just accept it? Do you also think that it is a form of "virtual cheating"? What is there to do? Thanks in advance.

That’s definitely a form of cheating! And in no way is that ok

There are different forms of cheating and from your post there does appear to be emotional cheating with the potential of physical cheating. Maybe a focus on what you would like from a relationship could be helpful. I always like to try and look at a scenario and reverse the roles, what if you looked at pictures of other people online for "diversity"? Surely he wouldn't mind if you were friends with them? Please don't think you should ever just "accept it".

There are different forms of cheating and from your post there does appear to be emotional cheating with the potential of physical cheating. Maybe a focus on what you would like from a relationship could be helpful. I always like to try and look at a scenario and reverse the roles, what if you looked at pictures of other people online for "diversity"? Surely he wouldn't mind if you were friends with them? Please don't think you should ever just "accept it".