I have seen it work both ways and it has worked both ways for me.  If you two are not meant to be together it wouldn't work out if you had or had not anyways.  If you want it to work out then just don't let it be an issue.  This is how I think of it for myself, if the dude cheats and we split up then he just lost the best thing he could have ever had.  It's on him and we apparently were not meant to be.  Thats it.