One of the most helpful things therapy can do for grief is simply create a space where it's allowed. Our social world is often impatient with grief. There's an expectation that it will resolve in a reasonable timeframe, that there are stages it will progress through, that we will arrive somewhere. This expectation is often more a comfort to others than a reality of mourning.
Grief takes as long as it takes. It changes shape over time, but it doesn't disappear. What therapy can offer is a space to feel it fully — without the social pressure to be further along than you are, without the need to protect others from how bad it actually is, and with someone who can sit alongside you in it without flinching.
The goal is not to get over a loss but to integrate it — to find a way to carry it as part of your life without it blocking your life. That's a different goal, and it's one that doesn't require betraying the love or the relationship that has been lost.