Should the occasion arise, feel free to use it.

Context is everything. These interactions are inappropriate because of your feelings and these feelings exist because of these interactions. Sending a McRib Meme isn't a problem on its face, but when he wants to put his reconstituted pork product in your sesame seed bun that meme is slathered in the BBQ sauce of betrayal.

You share a home and a life with a partner of 8 years. Giving room for another person to get between you is cheating. You've given oxygen to these feelings. Every conversation, message sent, meme shared, and stolen moment with this person is a conscious decision to betray your partner. This isn't an innocent crush where you like a coworker's personality and the way that their booty fills out their jeans. You've made many many small choices to get closer to this other person.

What do you mean by using you?

To me, this concept only really applies to young vulnerable girls who are being groomed and manipulated by an older guy. These boys or men use the girl's naivete against her. These men pretend that they are in love and in a relationship with these young people but only want nudes and sex, etc.

When we are talking about fully grown adults in their 20s, no one is getting used. Adults decide to have sex in the moment. It isn't transactional. The woman isn't exchanging sex for a committed relationship. Sex doesn't mean either of them is owed a long-term relationship. There is no inherent value in our sexy times. People aren't somehow diminished when they decide to f@#k.

I've been both 25 and 38. That's an inappropriate age gap.

Don't give in. Make your decision that it's over and then proceed accordingly. His protestations don't matter.

He doesn't need to understand anything

Texting is the lowest effort form of communication. It takes no time or energy to type out a few words and some emojis. You are being overly dramatic. He's not flooding your phone with messages. It shouldn't take 7 hours, let alone many days, to respond to a simple text. You are being discourteous.

This is an abusive relationship. Tell him that it's over. That is all. If he won't leave, contact law enforcement and have him removed.

This isn't a negotiation. All you have to do is tell him that it is over. He can't overrule your decision. It's over when you say it is.

As long as you completely and permanently remove that lying liar from your life, you can do whatever you want. Tell him or don't tell him, it's up to you.