While my wife won't let me fuck her ass, I can lick it, finger it and cum on it. She enjoys the hot slippery cum all over her her asshole and she rubs her cheeks around in it. She knows it makes me crazy to be able to do get her all slicked up and not be able to get it until she says I can. Sometimes its so hot looking, I stroke off another load of cum , as she spreads her ass open to catch it all. Sometimes she will rub a dildo in it and make me suck it. The best is when she is done buttering her ass with my cum. I finally get to get in there and lick it clean. This almost always leads to another cum shot right on her asshole, which she lets me get right away. If it were possible, I would do it all night long.
Does she take butt plugs or dildos up in her ass, but not your cock? If she doesn't even take them, try to get her to try them.... even privately at first. Once she discovers the joy of them, she may very well ask you to go deep into her.