the way I see it, if you want to be with him then you have to to come to terms with this. that means no calling him whenever you want it, no meetups as and when you feel like it. Yes, there will be times when you feel lonely and down but are the time spent with him all worthwhile to keep your relationship going? I know of someone who is involved with a married man for more than 10yrs and I can say that she is happy becos she has decided to be the "2nd woman". it is all about "acceptance of the situation" and your decision to make the best of it. if you can't come to terms with this and it is giving you a troubled life, then make a clean break from him and start living your life afresh :)
Any updates from TS? How did it go?