You have to work healthily on your resentment and get it out of your system, but you can't necessarily do it with him, because he is the instigator of your feelings.
I have a lot of resent for my "sufferer", I feel as though she disregards my feelings far too much to the point we can't really discuss them, I resent the fact she won't listen when I have listened to her, countless times.
I feel as though she has allowed somebody else to dictate our relationship, even forgetting how he treats her etc, I resent that she continues to allow them to do so, with absolutely no recourse for their behaviour.
I feel as though she is not being clear with me, I understand she can't necessarily give me an answer but I resent the fact that she can't at least tell me we may have a future or it is 100% done. Note what I say there, MAY have a future, I can take an I don't know right now that could still inevitably become a no anyway, but I resent that I feel as though I can't truly move forward. If we're finished for good, I can move on knowing that when I am ready I can start dating again, if she just said I don't know I'd not pine for her or pester, but I'd appreciate that perhaps I need to keep that in mind.
Holding on to all this, it hasn't helped, it's caused fights, it's caused issues that could have perhaps been avoided, it means I am holding on to some things, constantly letting that rot away and eat away at me. You have to find ways to work through that resentment, or you'll take it out on them, especially as they're inspiring it.
I've done the same, perhaps its understandable I feel these ways, but I suspect it's pushed a wedge between us that prevents some of what I want from actually happening.