what I’m getting is you love and value your DH, but life is long and yours has been tough recently.
20 year plus marriages aren’t necessarily exciting, and sometimes it’s tempting to get distracted by someone who isn’t him. I know this, no judgement. You also sound vulnerable, perhaps your self-esteem isn’t great, and there’s a type of man who can sense that, like sharks, one drop of blood in a hundred miles of dark water and they’re on their way.
Imagine the worse case scenario. Imagine your husband reading the messages you’ve already sent. ‘Stop watching me’ is flirting, if a dude was genuinely creeping you out you’d never send that and you’ve said you are attracted to him. It’s a risky little game you’re starting and I can guarantee you the prize is worthless.
Unless you want to end or, at a minimum, seriously damage your marriage, don’t engage with chappy anymore. Either block him or tell him next time he gets in touch that you’re happily married, love your husband and don’t want to hear any more from him. Imagine one day your DH will read what you’ve written. Write what you’d want to read if your DH was being targeted in this way by a married woman.
You need to be kind to yourself after everything, messing with this guy would be the exact opposite of that.