This is a hard situation to hear clearly when you are in the middle of it, so here is a straight read on what is actually happening.
Eight months in, a drug problem on her record, and she pivoted to another man the moment the money stopped. That is not a coincidence. Inmates, particularly those dealing with addiction, learn quickly who on the outside will keep their accounts funded and their commissary stocked. It is not always calculated in a cold way, but the pattern is real. People inside gravitate toward whoever makes their daily life more manageable, and money is the most direct way someone on the outside can do that.
If you want to re-engage, the practical moves are straightforward. Put money on her commissary account, send some letters that remind her of what you two actually had, and use InmateAid to send her something to read. Those gestures signal that you are still present and still invested without requiring her to make the first move after a falling out.
But go in with your eyes open. The man she turned to when you stepped back did not appear from nowhere, and there may be others. Inmates with active outside support networks sometimes have two or three people keeping their accounts running simultaneously, and none of them necessarily knows about the others.
None of that means the relationship is not worth fighting for. Only you can weigh that. What it does mean is that winning her attention back with money and letters is the easy part. The harder question is what this relationship looks like when she gets out, and whether the patterns you are seeing now are ones you can actually build something on.