I can understand MC keeping a low profile, that is helped from the fact he is famous for bringing resources, not beating dungeons or killing boss monsters.
He even acted together ith a party, so the fame was shared, and again, he didn't care about it.
I can understand him don't wanting to sound all pompous with his GF, and given what we see in this chapter is very likely she ignored half of the things he said, one thing is being against home dates, another to NEVER visit his house in years, that could have a possible explanation though, that when they started going out she did visit the place and when he got rich and moved she ignored it or thought it would have been a small upgrade, so she never got a glance to his new place.
Her deleting all his info does make sense, avoid troubles with your new guy and she thought nothing of him.
A thing people will soon realize is that her money sense got dulled by habit and ignorance, MC dates were all in luxurious places with a different atmosphere from where guild guy brought her, so she got used to them and thought they weren't actually high tier spots.
As NTR start is pretty forced because for a girlfriend of years to know so little it makes no sense, it would have been fine if it was months, 1 year, or MC had only recently raised to the top, they even got around often becasue MC loved her so the excuse of not talking enough doesn't hold up.