Whatever you do Kristl DON'T let him turn this situation around and put the blame on you, which by the statement he made, sounds exactly what he is trying to do, people are great at doing this, changing a situation that they are at fault, and turning it around to make you look like the one with the problem.

By all means address the concerns he has, but DON'T let him make you feel , you are the only one who needs to make changes, and make sure he does some soul searching too, and deal with this girl , if it causes you to be upset and rightly so, he should be MAN enough to say NO MORE, I love Kristl and her feelings are important to me, and I have to respect that and do the right thing and tell this girl to LEAVE ME ALONE.

You have invested three long years together, so do try and work things out by all means, just make sure he puts his full 100 per cent into the relationship as well, good luck dear.