“I love you but I’m not in love with you”
It’s a way of saying, I feel boredom, resentment or discomfort with this relationship. These things block the ability to feel intimate. Find out exactly what it is, so you can change it. Whatever it is she’s feeling, blame it on yourself. And hear her. But be optimistic. Don’t argue in any way. The more you argue, the more she will dig in her heels. The less you say the better - you’ll only give her ammunition. She’s the one who needs to do the talking.
There is a challenge that must be met for the relationship forward, and one or both parties can’t necessarily see their way to the other side. You will need to be the perpetual bearer of optimism on this front. Long-term relationships are statistically associated with male (not female) optimism and engagement. Weather her feelings are strongly negative or strongly positive, what is important is that she feels she can share, and feels that she was heard. Make her feel stronger and more confident, and you will be indispensable.
The appropriate route would involve gradually escalating emotional intimacy (communication), but give her whatever space she needs. Listen to her feelings, validate her feelings whatever they may be. They could be quite negative - simply be sorry that she feels that way. DO NOT take a Mr fix-it attitude or give her any advice, as she will later resent you advice even if she agrees in the moment. Listen. She is distressed, and when a woman is distressed, she want’s her man to be able to be her rock, her leaning-post. Strength in character is buoyant - you can infect her with your optimism gradually - if you can control your emotions better than she can, you have a chance. If she can infect your emotions with her negative feelings, she will see that you are weak of character.
Every time someone recites their thoughts and feelings, they become somewhat open to suggestion at the time, so that when it is stored again the thoughts are somewhat tampered with. In a given conversation it may seem like she is spewing negativity that is bottled up inside, but this is the moment when you can affect those thoughts with your positive outlook and perspective. She will remember that we talked about strong emotions she had for you together, and she could not bring you down with her negativity, you were there for her as her leaning post, exuding a loving feeling.
When she tests you, raining down negative emotions, she wants to see if she can deflate your optimism, see if you are weaker than her on the emotional level that she’s testing you on. Since women are physically weaker than men, they compete on an emotional indirect-aggression level. strength in character is more important to women than physical strength.
A woman may look for a man that is tall, strong, wealthy, etc. but if she can wreck him emotionally with some bombardment of hysterics, she will not respect him. She needs a man who can withstand the bombardment of other women’s tests, if she is to commit to him. Women can be very competitive with each other in the realm of indirect-aggression. She will test you herself to see what kind of bombardment you can shield her from. She may also play men against each other to see who is more dominant physically. Some women play these games better than others, but it would seem to be to their benefit.