I understand OP. I had 2 ONS before sleeping with the same man for 23yrs. I felt I was missing out through those 23 years, as I often wondered what it would be like with other men.
Sex with X had peaks and troughs, but was always safe and I could be me. It was great at times, crap at others. We tried all sorts and explored many things. We knew each others bodies so very well and knew the buttons to push to get things going.
After that ended, I went discovering! The thrill of the chase is fun. The new body is fun. But that's all it is, a momentary pleasure.
If you choose to meet people via a dating site, you get the build up of messaging, meeting for a coffee to see if you click, and if you do, the anticipation of meeting to take things further, then meeting again and again. Takes about 4-5 months for me for the excitement of that to pass.
If it's a ONS, then it's either really good or really crap during, but that pleasure and excitement is gone even quicker. Two of the men couldn't even remember my name the next morning. The one who was the best ONS I ever had was forgiven. The other couldn't get an erection, so he was not forgiven!
I'm currently with a FWB, met online, been seeing him on and off for 3 years. Not serious. We're both looking elsewhere. But because we've been having sex so long, and have a good friendship, sex with him is better than any ONS, as it's engaging, it's funny, we know what the other likes, cuddly wake ups are lovely and we respect and care for the other.
So having said all that, my advice is to keep it as a thought. Don't act on it. The momentary pleasure is a real high, no denying it. But that's all it is. IMO, it's not worth risking the long term love and care for a short time physical high.