After these many years, I think I am finally seeing what could possibly be your future.
I was always somewhat perplexed by the way Sue seemed to react to you lately (the last several years). As told through your thread, she seemed at times to be harsh, somewhat humiliating (though always only to you, in private), yet loving. I mentioned early this year that she seemed to be willing to have sex with you bare, but it was not her ideal, and seemed to be a "mercy fuck". She always said she was available to you if you needed it, but it wouldn't be her choice, and she would do everything to lay a guilt trip on you and smile when you chose to use a condom. I at times thought she was using "the two steps forward, one step back" approach on you. I was also mystified by your always relating that she was happy your cum was not ending up in her pussy: it was either in a condom, or on your belly after a Wednesday night ritual, and eventually found it's way into your mouth.
I wondered what was Sue's motive? Could she despise you so much that she couldn't stand the thought of your cum in her pussy - but that didn't fit with her love for you. Was Sue playing with you psychologically, to enhance your 'Beta' feeling by "playing" as if she never wanted to have your cum in her pussy? Or is this really her feeling due to her new Alpha status, to your Beta status, and replacing you sexually with a better, more virile lover.
I finally believe it is the third. You have spent years getting to this point; encouraging Sue to take other men for lovers, and trying to make her understand it arouses you. You have handed Sue the reins, and allowed her to assume the Alpha role, as you yourself have told her you want to be the Beta role in your relationship. It took many years for Sue, wondering what you were doing, and going along yet trying not to hurt you in the process, but Sue now sees she has the best of all worlds. You have repeatedly told her you wanted her lover to be her primary sexual partner, and have told her how her denial of you arouses you, and makes you happiest.
Sue has you as a loving, supportive husband, and father to your children. You have good employment, provide shelter, food and clothing, and very good companionship. On top of that, you have allowed her to seek out and have lovers, several of which have been much better than yourself. She has your love and support, and yet can indulge her sexual urges to her hearts content, without any recriminations. And she has done quite well most of the time, with the last three major lovers, Frank, Robert, and now Paul, providing as much sex as she wants and can get. I remember her taking a five day trip to Atlantic city with Frank, and having enough sex that Frank came on average twice a day, and once three times in a day. Robert was well endowed, better than you if your reports are correct, and he could go two or more times in a day. Paul seems to go two or more times in a day, seems to have fucked her 8-10 times in a four-day golf weekend in SC, and has the stamina to go for several hours, with appropriate breaks, and as you reported yesterday, to "fuck the shit" out of Sue.
This isn't all bad though. As you yourself have repeatedly reported in your thread, and through your conversations with Sue, this mutual arrangement seems to arouse both you and Sue. You get great enjoyment thinking of what you have given up, and allowing Sue to give her pussy exclusively for Paul's use. Sue gets aroused that she is allowed to have sex with her lover, with her husband's permission, and the husband is turned on by being denied sex with his wife.
Sue has slowly upped the ante in this arrangement, first denying you for several weeks, then several months, at a time. Then she convinced you to use condoms, and has really only had bare sex with you less than 10 times in the past two years - and this arouses you. Sue has asked you repeatedly about the enjoyment you get with masturbation, encouraged you to masturbate as often as you want, as a subsitute for interacting with her sexually. Now Sue had you shaving your genitals knowing that it would make you self-concious of your pubescent look compared to Paul's manscaping, which has had the effect of making your genitals more sensitive, and yet you are less willing to let Paul see your shaved look, so you stay on the periphery of their sexual encounters, where Sue deems she wants you.
What does this all mean? I believe your future is as a Beta, to Sue's Alpha, and Sue's lover(s). Sue has stated that the dynamic has changed, that the two of you don't have the same "synch" anymore, and that is how she wants it. She has told you in subtle terms that she wishes you would accept your role, relax, and forego sex with her, with or without a condom, in the future. Sue will get all of her sexual satisfaction from her lovers. Paul is the current lover, and I honestly don't see that changing for a good long time. Sue may tire of Paul over the long haul, but I really see this going beyond next spring, slowing down only when the kids are around (summer), but going full blast while you are empty-nesters, until Paul does something that makes Sue back away and seek termination of their relationship. However, Sue will then hunt a new lover, and again will be looking for youth, stamina, and inventiveness, to satisfy her cravings.
You STB, will be relegated to masturbation as long as Sue has a lover. Only during those "between times" will Sue seek you out for sexual satisfaction, and only with a condom. You will only get Sue's pussy bare, if and only if Sue desires it (which as you admit, may be forever), or...if you decide to become the Alpha again to Sue. I don't see that happening. You just went through a family crisis, and you may have exhibited Alpha characteristics to help Sue, her mom and sisters through it, but I don't see you desiring to be the Alpha in your sexual relationship with Sue. Even if you decide to become the Alpha, I believe Sue will test you extensively, and in many ways.
Finally, I make one last suggestion... buy Paul a robe to use at your house. But don't just buy any robe (don't get a thin, plaid robe). Get a nice fluffy one, white with navy or red piping, or red, navy blue or even "royal purple" (to mark it's importance), with Paul's initials embroidered on the left breast of the robe. That way he isn't borrowing your robe, and it hangs in your bedroom to remind you of his presence in Sue and your relationship. You might present it to them (Sue and Paul) for Sue's birthday, or as an early Christmas present.