You know what's the situation. There's no free meal in this world. The more you accept favours/ help from him, the more you'll feel compelled to reciprocate - meaning, to accept or agree to the "simple" things he ask of you.

I'm sure you can find someone else to help with your Academics. Pretty sure you don't need him. Part of you wanted to cling on him for some reason, and imo, using academics as an excuse maybe? Imagine if he didn't appear in your life at all. How would you handle your Academics? Are you going to flunk it?

If you can sense the other person has ulterior motive and yet, you still accept his help/ favour and advances, then it's obvious what road you have chosen.

Otherwise if you're really not interested,
- just cut down the chatting and go straight to academics
- whenever he flirts, just avoid it and divert straight back to main topic
- reduce the frequency of chatting with him
- show that you're disinterested in his advances
- turn him down
- discourage whenever he makes a move
- lastly, casually point out that he's married with kids and that he should stop all these flings for the sake of his family

On this... there are different school of thoughts imo.

Some feel that emotionally involved is also considered cheating. Example, even if they couldn't meet physically and be intimate, doing so over the phone (flirting, love talk) etc emotionally - it's also cheating. So whether she flirted back or not - only TS will know. On the other hand, whether the guy misinterpreted her friendliess or took advantage of TS's situation - this is another question mark.

Also, my suspicion only... TS may not have been entirely honest about the situation. Probably start to feel some sort of guilt that the guy has a family, and yet, still somewhat interested in him.