Son is probably happy getting to spend so much time with OD. It must seem a little strange eclipsing all of 2018’s visits in one go. Sounds like they both had a good time.
I agree with others, OW must be on the outs.
I am with you, something is going on. Is this incipient reconnect or a something else. Time will reveal I suppose.
DnJ
Feelings are fleeting. Be better, not bitter. Love the person, forgive the sin.