After years of almost no sex with your SO I believe you're entitled to seek sexual satisfaction and physical intimacy elsewhere.
Believe me I felt no guilt at all.
But getting "permission" from your SO will likely blow up in your face, and if you're used to SP's and SB's, etc., etc., seeing only MP's will probably not be sufficient to satisfy your needs.
You've gotten away with it so far, and it seems on a grand scale. Just keep doing what you're doing, like 99% of the rest of us here do, and keep it on the "down low"...