I see no progress here. I see no evidence of this situation changing for the better or any solid attempt on your part to sort this out. You are just going over old ground with a few new bits of information now and then which, to be perfectly honest, does nothing to help resolve your current situation.
I
do sympathise, believe me. But all I see is A LOT of talk and no action.
There is however A LOT of good advice in this thread. You really should have confronted her by now. I simply do not understand why you haven't done so. I’m not talking about the "evidence" you may have regarding the potential cheating lark but the state of the relationship itself. Just simply talking about your relationship with her may reveal hidden truths naturally, while although painful to hear, will provide a certain amount of relief for yourself and your partner.
Not knowing, as I'm sure you understand, is one of the hardest elements you have had to deal with. However, you don’t know what she’s going through. She could be just as traumatised about this situation and is desperate for a way out. The fact that you both live together makes things that much more difficult.
This is end game. Perhaps meeting somewhere neutral would help, go for a quiet drink somewhere and lay all cards on the table. Simply ask her “Do you want to work things out, try and salvage our relationship or call it a day? Be honest.” Or something along those lines.
In closing, I feel there is too much mistrust, doubt and a sprinkling of paranoia (perhaps justified, perhaps not) for this relationship to continue. In the future, who knows… time does wonders for all kinds of emotional ailments.
Please, for your own mental health if nothing else, just get this sorted. NOW.