What are some tips to make him see that I won't fall in love all over again?
... er, get on with your life.
If he pursues you or engages in flirting or encouraging language, be honest rather than just ignoring it.
(I'm assuming the in love... again is that you both have some history together)
"Tom, look, thanks for taking an interest in me, but seriously, it's just not something I want or appreciate."
If he doesn't take the strong hint, then escalate.
"Tom, please, I've tried to make it clear that I'm not interested. Please do not contact me or try to engage with me."